2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

1

OSAC 2020-S-0003

Guidelines for Performing 

Alcohol Calculations in 

Forensic Toxicology

Forensic Toxicology Subcommittee

Chemistry: Seized Drugs & Toxicology Scientific Area Committee (SAC)

Organization of Scientific Area Committees (OSAC) for Forensic Science
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

2

OSAC Proposed Standard

OSAC 2020-S-0003

Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

Prepared by 

Forensic Toxicology Subcommittee

April 2022

Disclaimer:

This OSAC Proposed Standard was written by the Forensic Toxicology Subcommittee of the 

Organization of Scientific Area Committees (OSAC) for Forensic Science following a process that 

includes an open comment period. This Proposed Standard will be submitted to a standards 

developing organization and is subject to change. 

There may be references in an OSAC Proposed Standard to other publications under development by 

OSAC. The information in the Proposed Standard, and underlying concepts and methodologies, may 

be used by the forensic-science community before the completion of such companion publications.

Any identification of commercial equipment, instruments, or materials in the Proposed Standard is 

not a recommendation or endorsement by the U.S. Government and does not imply that the 

equipment, instruments, or materials are necessarily the best available for the purpose.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a Scientific 

and Technical Review Panel (STRP). The STRP process is vital to OSAC’s mission of

generating and recognizing scientifically sound standards for producing and interpreting forensic

science results. The STRP shall provide critical and knowledgeable reviews of draft standards or of 

proposed revisions of standards previously published by standards developing organizations (SDOs) 

to ensure that the published methods that practitioners employ are scientifically valid, and the 

resulting claims are trustworthy.

The STRP panel will consist of an independent and diverse panel, including subject matter experts, 

human factors scientists, quality assurance personnel, and legal experts, which will be tasked with 

evaluating the proposed standard based on a comprehensive list of science-based criteria. 

For more information about this important process, please visit our website at: 

https://www.nist.gov/topics/organization-scientific-area-committees-forensic-science/scientifictechnical-review-panels
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

3

Guidelines for Performing Alcohol Calculations in Forensic Toxicology

Foreword

Forensic toxicologists and other experts are frequently requested to perform calculations related to 

alcohol (ethanol), but there can be a high degree of variability in how this work is performed. 

Adherence to this guideline will improve the quality and consistency of this type of work that could 

mitigate the risk for bias.

There are numerous factors that must be taken into consideration when providing estimates related to 

alcohol consumption and alcohol concentrations. Alcohol pharmacokinetics vary within the 

population, but also within an individual. A person’s exact volume of distribution and elimination rate 

at a given time cannot be known. Many forensic blood alcohol results are based on replicate analyses 

and are reported with an estimation of measurement uncertainty, however, many other results (e.g. 

breath tests, medical tests) may not provide an uncertainty. Other factors in the process, such as time 

and weight, may have unknown degrees of accuracy associated with them, depending on the source of 

the information. These factors do not prohibit reasonable estimates from being determined, but do 

require experts to be conservative, knowledgeable about the limitations, and thorough in their work. 

The expert should not overstate the interpretation of their calculations; nor should they oversimplify 

the process.

The approach taken in this guideline is to provide a reasonable estimate of the range which 

encompasses the value of interest, and then apply that range to the question at hand, with 

consideration of the assumptions that may/may not be made. For example, in a situation where there 

is a long delay between the incident and the blood draw, an expert may be asked what the subject’s 

blood alcohol concentration was at the time of the incident. Due to the factors discussed within this 

guideline, the science does not support being able to provide a single value. Rather an estimated range 

can be provided and applied to the case at hand, while clearly stating any assumptions that may impact 

that application. The range does not put any greater likelihood that the subject was at the high or low 

end of the range, nor that they were likely in the middle. The Appendix illustrates how this approach 

can be applied in various scenarios.

Future editions of this guideline will work toward applying a statistical approach to the calculations. 

There are approaches in the literature that provide estimated uncertainties for some of the variables 

contained within the calculations. For example, for elimination rate and volume of distribution, there is 
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

4

a significant amount of scientific literature that one may be able to reasonably estimate an average with 

an associated uncertainty. The body of knowledge in the peer reviewed literature is continually 

increasing and may eventually allow for estimations of the variances associated with all the 

parameters. 

Personnel and training requirements are outside the scope of this guideline. It is expected that persons 

performing this type of work have an understanding of pharmacokinetics, along with relevant 

education and experience. 

Keywords

Alcohol (ethanol), retrograde extrapolation, pharmacokinetics

Table of Contents

1. Scope

This document provides guidelines for performing alcohol (ethanol) calculations. Guidance on 

calculations for retrograde extrapolation, forward estimations, minimum drinks consumed, and 

other typical situations are addressed. Recommendations are provided for evaluation of post 

absorptive stage, various specimen types, and population variances. Reporting of calculations is 

also addressed. This guideline is intended for an expert performing alcohol calculations, whether 

as an employee of a public or private laboratory, or as an independent forensic service provider. It 

applies to matters related to criminal and/or civil proceedings.

2. Normative References - Required references for using this guideline

Maskell, P., Jones, W., Savage, A., and Scott-Ham, M. Evidence based survey of the distribution volume 

of ethanol; comparison of empirically determined values with anthropometric measures. Forensic 

Science International, 2019.

Jones, A.W. Pharmacokinetics of ethanol – Issues of forensic importance, Forensic Science Review, 

2011.

3. Terms and Definitions

3.1. Alcohol = ethanol
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

5

4. Background Information

4.1. Alcohol Pharmacokinetics

The mechanisms of absorption, distribution, and elimination of alcohol throughout the body 

must be considered when performing alcohol calculations.

4.1.1. Absorption

The absorption of alcohol is a complex dynamic process that begins as soon as drinking 

begins. Alcohol is primarily absorbed into the blood stream through the small intestine, 

but some absorption occurs in the stomach and mouth. Absorption rates are highly 

variable and are not linear. Factors such as the presence of food in the stomach, the 

type and volume of beverage consumed, other drugs consumed, and the condition of the 

gastrointestinal tract, can impact the rate of absorption. Studies support that it can take 

up to 2 hours for complete absorption after the last drink. (2-4, 7-9, 12, 14-16, 19, 23,

24, 30, 31, 34) The time needed to reach the peak alcohol concentration (AC) is not the 

same as the time to complete absorption.

4.1.2. Distribution

Alcohol is water soluble and rapidly distributed throughout the total body water by the 

blood supply. For alcohol, the volume of distribution (Vd) is closely correlated with the 

total body water. Numerous factors impact an individual’s Vd including sex, body mass 

index (BMI), and age. In general, Vd is typically lower for women, obese individuals, and 

the elderly. Numerous publications propose mathematical approaches to estimate an 

individual’s Vd based on certain factors (height, weight, sex), and attempt to provide 

ranges for the Vd of alcohol. (5, 18, 25, 28, 29) However, there are significant 

limitations to these studies. For example, the number of participants in many studies is 

quite small, and the ethnic diversity is often unknown. There are also differences in 

whether Vd, total body water, or rho were measured. Some involved bolus drinking, 

while others used a social drinking scenario. Alcohol concentration may have been 

measured in whole blood, serum/plasma, or breath. (5, 18, 25, 28, 29) Therefore, 

caution must be used when comparing, or attempting to average, these various formulas 

since they do not all calculate the same variable.

4.1.2.1 Research supports a range of 0.40 – 0.80 L/kg or an anthropometric approach 

(normative references 1 and 2). 

4.1.2.2 Maskell, et al (normative reference 1) determined the accuracy and precision of the 

various equations to estimate a subject’s Vd by applying them to a single data set 

compiled from six published studies. The authors provide suggested correction 
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

6

factors for bias, along with confidence intervals for each model. This approach 

considers the subject’s individual factors and provides a range of Vd values to apply 

in further calculations.

4.1.2.3 Due to the high variability among the population, the use of a single factor for Vd is 

inappropriate. 

4.1.3 Elimination

Alcohol is primarily eliminated via enzyme metabolism in the liver; however, a small 

amount is removed through first pass metabolism or excreted unchanged in the breath, 

sweat, oral fluid, and urine. Alcohol is eliminated at a constant, linear rate (zero order 

kinetics), until low concentrations are reached. The linear rate can only be applied 

when elimination is the only pharmacokinetic parameter occurring, in other words, the 

subject is post absorptive. While the AC may be declining after the subject reaches their 

peak AC (post peak), the linear rate is not applicable until the post absorptive state.

4.1.3.1 An elimination rate range of 0.010 – 0.025 g/dL/hour encompasses the majority of 

the population regardless of age, sex, ethnicity, and drinking experience. (normative 

reference 2, and 10, 11, 13, 20, 21, 26, 32)

4.1.3.2 At concentrations below 0.020 g/dL, the elimination rate may not be linear as zero 

order kinetics may no longer apply. (1, 11)

4.2 Case History

The type of information, and source of that information, will vary from case to case. Experts 

should be clear as to the information they rely upon, and the assumptions they make. On 

occasion, that information may change as the case proceeds. 

4.2.1 Time: the time of the incident and the timing of drinking play a role in the

assumptions that can be made and the associated calculations. For example, 

the time of last drink based on video surveillance may be considered 

differently than a time based on the subject’s self-reported drinking history. 

This may impact the assessment of whether the subject was post absorptive 

at the time of the incident. 

4.2.2 Type of beverage: when there is evidence of the type of beverage consumed, it 

may be appropriate to calculate the number of drinks based on that 

information. However, in other situations, it may be more appropriate to 

reference a “standard drink” (see 4.5), such as when there is no history, or the 

subject consumed unknown quantities of various types of drinks.
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

7

4.3 Specimen Considerations

4.3.1 Serum and plasma have a higher water content than whole blood. Research supports a 

serum/plasma to blood ratio of 1.04 to 1.26. (6)

4.3.2 Urine is an elimination product which is influenced by hydration and time since last 

void. Results from urine alcohol testing are not amenable to extrapolation or other 

calculations, including urine results that have been converted to a whole blood 

equivalent.

4.4 Propagation of Uncertainty

The variance and distribution for all parameters used in the calculations has not been fully 

characterized in the scientific literature at this point. Therefore, as an initial minimum 

guideline, a statistical approach incorporating the uncertainties for each of the parameters is 

not presented. This guideline does not prohibit the expert from applying accepted statistical 

models within the calculations. These calculations should be clearly presented, with references 

or stated assumptions for the associated uncertainties and the method of determining the 

uncertainty. 

If known, the range associated with the measurement uncertainty of the test result may be 

incorporated.

4.5 Standard drink

A “standard drink” is defined as a beverage containing approximately 14 grams of alcohol. (33)

e.g. 12 ounces, 5% beer

5 ounces, 12% wine

1.5 ounces, 80 proof liquor (40%)

4.6 English/Metric conversions (if applicable)

Volume: 1 ounce = 29.6 mL

Weight: 1 pound = 0.454 kilograms

Height: 1 inch = 2.54 centimeters or 0.0254 meters

4.7 Density of alcohol = 0.789 g/mL

5 Calculations

5.1 Alcohol Test Results
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

8

5.1.1 Calculations presented are valid for both blood (g/dL) and breath (g/210L).

5.1.2 Serum/plasma results shall be converted to a whole blood equivalent prior to other 

calculations. The range should be 1.04 to 1.26 serum/plasma to blood ratio. (6) Further 

calculations shall then be applied to both converted AC results.

5.2 Widmark’s Formula – the relationship between a dose of alcohol and a resulting alcohol 

concentration. 

Equation 1

where:

AC = alcohol concentration (g/L)

D = dose (g)

Vd = volume of distribution (L/kg)

w = weight (kg)

Variations of the formula can be applied to several common scenarios. 

Estimating the minimum number of drinks to achieve a particular alcohol concentration may be

used to support/refute a particular drinking history, or to establish that someone could not 

have consumed less than that amount of alcohol.

5.2.1 Theoretical minimum number of drinks to achieve a particular alcohol concentration:

This calculation does not account for any drinks eliminated. It provides an estimate of 

the equivalent dose of alcohol in the system at the time of the blood draw/breath test.

Equation 2: Minimum dose of alcohol

D = AC × Vd × w × 10dL

L where:

D = dose (g)

AC = alcohol concentration (g/dL, g/210 L breath)

Vd = volume of distribution (L/kg)

w = weight (kg)

Equation 3: Using the calculated dose to estimate the minimum number of “drinks” 

when beverage concentration is known

V =

D

C × ρ × m

where:

Vd w

D

AC

*

=
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

9

V = volume (oz)

D = dose (g)

C = beverage concentration (mL/100mL)

ρ = density of ethanol (0.789 g/mL)

m = metric conversion (29.6 mL/oz), if necessary

The calculated volume can be converted to the equivalent number of drinks, depending 

on the type of drink. e.g., If the subject was drinking 12 oz beers, a volume of 37 oz 

would be equivalent to ~ 3 beers.

5.2.2 Maximum alcohol concentration that could theoretically be achieved from a given dose:

These calculations provide the maximum AC attainable from a reported number of 

consumed drinks. They are used to support/refute a particular drinking history. The 

calculations are used to attempt to answer the question: “If someone had X number of 

drinks, could they have reached the measured AC?” The calculated results can also 

provide information to account for potentially unabsorbed alcohol or post incident 

alcohol consumption. 

Equation 4: Dose of alcohol from a drink

D = V × C × ρ × m

where:

D = dose (g)

V = volume (oz)

C = beverage concentration (mL/100mL)

ρ = density of ethanol (0.789 g/mL)

m = metric conversion (29.6 mL/oz), if necessary

Equation 5: Theoretical maximum AC from a given drink(s)

This calculation provides the theoretical maximum alcohol concentration. It assumes full 

absorption with no elimination.

ACdrink(s) =

D

Vd × w × 10 dL

L

where:

ACdrink(s) = max alcohol concentration (g/dL) from a drink(s)
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

10

D = dose (g)

Vd = volume of distribution (L/kg)

w = weight (kg)

5.2.3 A range shall be used for Vd in the calculations; either a range of 0.40-0.80 L/kg, or the

calculated range using an anthropometric approach (see 4.1.2.1).

5.2.4 See A.1 for examples

5.2.5 Alcohol eliminated during the drinking timeline may be further considered if 

necessary/applicable.

5.3 Retrograde Extrapolation

Retrograde extrapolation is a mathematical process that uses an alcohol concentration at a given 

point in time and estimates what the concentration would have been at an earlier time.

NOTE: It is not possible to calculate the exact alcohol concentration at an earlier point in time, but

an estimation in the form of a range of concentrations can be provided. 

5.3.1 Basic Calculation

Equation 6:

ACinc = ACtest + (R × T)

where:

ACinc = estimated alcohol concentration at the time of the incident (g/dL)

ACtest = measured alcohol concentration (g/dL)

R = elimination rate (g/dL/hour)

T = time between incident and time of breath test/blood draw (hours)

5.3.2 Extrapolation shall not be performed on alcohol concentrations below 0.020 g/dL.

5.3.3 Elimination Rate Range

5.3.3.1 The calculation shall be performed using a range of elimination rates. The minimal 

range shall be 0.010 – 0.025 g/dL/hour.

5.3.3.2 An elimination rate calculated from two or more test results shall not be used in 

place of a range. 

5.3.4 Assessment of absorptive state

5.3.4.1 The impact of potentially unabsorbed alcohol shall be addressed. 

5.3.4.2 If the time of incident is more than 2 hours after the time of drinking cessation, it is

reasonable to assume the subject is post absorptive. See A.2 for example.
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

11

5.3.4.3 When the drinking history is unknown, it is not reasonable to assume that the 

subject is only post absorptive. Additional calculations can be applied to assess the 

impact of potentially unabsorbed alcohol. See A.5 for example.

5.3.4.4 If case history indicates that alcohol was consumed after the incident, but before the 

sample was obtained, this shall be accounted for in the estimates. 

5.3.4.5 An option to account for unabsorbed alcohol or post incident alcohol consumption is 

to subtract the impact of those drinks from the estimated post absorptive alcohol

concentrations (determined from Equation 6). See Equation 4 to calculate the 

maximum AC contribution from a drink. 

Equation 7:

Adjusted ACinc = ACinc – ACdrink(s)

where:

Adjusted ACinc = estimated AC at time of the incident, accounting for potentially 

unabsorbed alcohol or post incident alcohol consumption

ACinc = estimated AC at time of the incident if subject were in post absorptive 

state (calculated from Equation 6)

ACdrink(s) = maximum AC contribution from drink(s) (calculated from Equation 5)

Reference A.3 for example of subject not being post absorptive. See A.4 for example 

of post incident alcohol consumption.

6. Additional Considerations and Best Practice Recommendations

6.1 Documentation: Calculations should be documented, and assumptions clearly stated. This may 

be in the form of case notes, an electronic spreadsheet, a written report, etc.

6.2 Protocols: It is recommended that written protocols be in place to ensure the forensic service 

provider applies a consistent methodology to service requests. 

6.3 Technical Review: Where feasible, independent review of calculations by a qualified individual 

is encouraged.

6.4 Calculations during testimony: Performing alcohol calculations is a forensic service request, 

and should not be viewed as just a question during direct or cross examination, or “simple 

math” that the expert should be able to readily perform in their head. While the expert must 

respectfully follow the orders of the legal authorities overseeing the testimony (trial, 

deposition, etc), performing calculations during live testimony is discouraged due to the various 

risks to quality it may create. When so compelled, it is recommended that the witness 

document the additional work. Depending on the scope of the new work request and the 
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

12

complexity, the expert may consider requesting a brief recess to perform the work. In some 

circumstances, it may be appropriate to discuss the impact a change would have on the 

calculations, rather than redoing them all, e.g., if the subject’s drinking history changes, one 

could state that it would raise/lower the estimated AC range provided. 

6.5 Postmortem specimens: The principles and practices outlined in this guideline may also apply 

to postmortem scenarios, but there are additional variables to be considered that are outside 

the scope of this guideline. (18,23)
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

13

Appendix A (examples)

NOTE: The Appendix is intended to provide illustrative examples to apply the recommendations

contained within the guideline; it does not represent the only way the recommendations may be 

applied or presented.

A.1. Support/refute drinking history

History: A 32-year-old male subject was pulled over for suspected impaired driving. He had an 

evidential breath test result of 0.19g/210L. He stated he had been at a local bar for the last 3 hours and 

only had 2 pints of Brand X beer. He ate chicken wings and french fries.

Question: Is the stated drinking history consistent with the AC result?

This can be answered two different ways: by calculating the minimum number of drinks 

needed to attain a certain AC, or by calculating the maximum AC attainable from a drinking 

history.

Relevant Information: 

The subject is 6’1”, 230 lbs

Evidential breath test: 0.19g/210L

Alcohol content of Brand X beer ~4.3% (cite reference for that brand’s alcohol content (e.g. 

internet site and access date, published reference))

1 pint = 16oz

Calculations:

Weight conversion: w = 230 lbs × 0.454 kg

lbs = 104 kg

A.1.1 What is the minimum number of drinks needed to reach a 0.19g/210L AC?

Using Equation 2 and a Vd range of 0.40-0.80 L/kg, calculate the dose needed:

D = AC × Vd × w × 10dL

L

D = AC × Vd × w × 10dL

L

D = 0.19 g

dL × 0.40 Lkg × 104kg × 10dLL

D = 0.19 g

dL × 0.80 Lkg × 104kg × 10dLL

D = 79g D = 158g

Using Equation 3, calculate the equivalent number of drinks for that dose: 

V =

D

C ×ρ ×m

V =

D

C ×ρ ×m

V =

79g

4.3

mL

100mL ×0.789 gmL ×29.6

mL

oz

V =

158g

4.3

mL

100mL ×0.789 gmL ×29.6

mL

oz
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

14

V = 79 oz V = 157 oz

Drinks = 79oz / 16oz = 5 pints Drinks = 157oz / 16oz = 10 pints

Opinion: The subject’s stated drinking history is inconsistent with the breath test result. He had the 

equivalent of ~5-10 pints of Brand X beer in his system at the time of the test.

A.1.2 What is maximum AC that could be reached from 2 pints of Brand X beer?

Using Equation 4, calculate the dose from 2 pints of Brand X beer:

D = V × C × ρ × m

D = 32oz × 4.3

mL

100mL

× 0.789 g

mL

× 29.6

mL

oz

D = 32g alcohol in 2 pints of Brand X

Using Equation 5 and a Vd range of 0.40-0.80 L/kg, calculate the maximum range of ACs this 

dose could theoretically reach:

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

32g

0.40 L

kg×104kg ×10 dLL

ACdrink(s) =

32g

0.80 L

kg×104kg ×10 dLL

ACdrink(s) = 0.077g/dL ACdrink(s) = 0.038g/dL

Opinion: The subject’s stated drinking history is inconsistent with the breath test result. If all the alcohol 

in 2 pints of Brand X were completely absorbed, and none eliminated, the maximum AC range achievable 

for the subject would be ~0.038-0.077 g/dL. 

A.2. Retrograde extrapolation, subject is post absorptive

History: A 45-year-old woman was drinking wine at an out of town wedding. She left the wedding at 

6:00 pm, and had a five-hour drive home. At approximately 9:00 pm she crossed over the center line 

and crashed into an oncoming vehicle. She was injured and transported to the hospital; a blood kit was 

collected at 11:45 pm. The result of the blood test was 0.068g/dL. There were no alcoholic beverages 

in the vehicle. She stated she had not had anything to drink since leaving the wedding.

Question: What was her AC at the time of the crash? 

Relevant Information: 

The subject is 5’3”, 125 lbs

Blood alcohol: 0.068g/dL at 11:45 pm
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

15

Incident: 9:00 pm

Assumptions:

Since there were at least 3 hours between the end of drinking and the incident, the subject is 

assumed to be post absorptive.

No post-incident alcohol consumption.

Calculations:

Elapsed Time = 9:00 pm to 11:45 pm = 2.75 hours

Using Equation 6 and an elimination rate range of 0.010-0.025 g/dL/hour, calculate AC range at 

time of incident:

ACinc = 0.068 g

dL + (0.010 gdL/hour × 2.75 hours) = 0.096 gdL

ACinc = ACtest + (R × T)

ACinc = 0.068 g

dL + (0.025 gdL/hour × 2.75 hours) = 0.137 gdL

Opinion: It is estimated that the subject’s AC at the time of the incident was ~0.096-0.137 g/dL. Therefore, 

it is likely the subject was above the 0.08 g/dL legal limit at the time of the incident.

A.3. Retrograde extrapolation, subject is not post absorptive

History: A 22-year-old female subject was drinking tequila shots at a bar. She paid her tab, took one 

last shot, and left the bar at ~11:00 pm. She crashed her car while trying to leave the parking lot. Her 

blood was drawn at 12:30 am and was a 0.082 g/dL. Her defense is that she was below 0.08g/dL at the 

time of the crash.

Question: Could the subject’s AC have been under 0.08 g/dL at the time of the crash?

Relevant Information:

The subject is 5’8”, 160lbs

Blood alcohol content: 0.082 g/dL at 12:30 am

Incident: 11:00 pm

80 proof = 40% alcohol concentration

Assumptions:

The alcohol from the last shot of tequila was not absorbed at the time of the incident.

Tequila is typically ~80 proof.
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

16

Calculations:

Elapsed Time = 11:00 pm to 12:30 am = 1.5 hours

Weight conversion: w = 160 lbs × 0.454 kg

lbs = 73 kg

Using Equation 6 and an elimination rate range of 0.010-0.025 g/dL/hour, calculate AC range at 

the time of incident, if the subject were post absorptive:

ACinc = 0.082 g

dL + (0.010 gdL/hour × 1.5 hours) = 0.097 gdL

ACinc = ACtest + (R × T)

ACinc = 0.082 g

dL + (0.025 gdL/hour × 1.5 hours) = 0.120 gdL

Using Equation 4, calculate the dose of alcohol from a shot of tequila:

D = V × C × ρ × m

D = 1.5oz × 40 mL

100mL

× 0.789 g

mL

× 29.6

mL

oz

D = 14g alcohol in shot of tequila

Using Equation 5 and a Vd range of 0.40-0.80 L/kg, calculate the maximum AC a tequila shot 

could contribute:

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

14g

0.40 L

kg×73kg ×10 dLL

ACdrink(s) =

14g

0.80 L

kg×73kg ×10 dLL

ACdrink(s) = 0.048g/dL ACdrink(s) = 0.024g/dL

Using Equation 7, adjust the AC to remove the theoretical maximum contribution the last shot 

could have contributed (using the calculated ranges of ACinc and ACdrink(s)):

Adjusted ACinc = 0.097 – 0.048 = 0.049g/dL

Adjusted ACinc = ACinc – ACdrink(s)

Adjusted ACinc = 0.120 – 0.024 = 0.096g/dL

Opinion: Assuming the last shot of tequila was not absorbed at the time of the incident, the subject’s AC at 

that time is estimated to be ~0.049 – 0.096g/dL. Therefore, it is possible she was below the 0.08 g/dL legal 

limit at the time of the incident.
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

17

A.4. Post incident consumption

History: A 55-year-old man drove his vehicle through his garage door at ~6:00 pm. A neighbor 

witnessed the crash and called the police. When the police arrived at the home, the subject greeted 

them with a partially consumed bottle of vodka in his hand (80 proof, 750 mL), and he appeared to be 

intoxicated. He was arrested for suspected DUI and had a breath test result of 0.215 g/210L. The 

defendant claimed he had not been drinking prior to the crash, and that his AC was from the vodka 

consumption after the crash. He claimed it was a new bottle; approximately one-third was missing.

Question: Could the consumption of 1/3 bottle of vodka account for the measured AC?

Relevant Information:

The subject is 5’10”, 210 lbs

Breath test result: 0.215g/210L

80 proof = 40% alcohol concentration

Calculations:

Weight conversion: w = 210 lbs × 0.454 kg

lbs = 95 kg

Amount consumed = 750 mL x

1

3

= 250 mL

Using Equation 4, calculate the dose of alcohol from the vodka

D = V × C × ρ (metric conversion not needed)

D = 250mL × 40 mL

100mL

× 0.789 g

mL

D = 79g alcohol in 1⁄3 bottle of vodka

Using Equation 5 and a Vd range of 0.40-0.80 L/kg, calculate the maximum AC the vodka could 

contribute:

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

79g

0.40 L

kg×95kg ×10 dLL

ACdrink(s) =

79g

0.80 L

kg×95kg ×10 dLL

ACdrink(s) = 0.208g/dL ACdrink(s) = 0.104g/dL

Using Equation 7, adjust the AC to remove the contribution from post-incident alcohol 

consumption (using the calculated ACdrink(s) range): 
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

18

= 0.215 –0.208 = 0.007g/dL

Adjusted ACinc = ACinc – ACdrink(s)

= 0.215 –0.104 = 0.111g/dL

Opinion: If all the alcohol from the 1/3 bottle of vodka were completely absorbed, and none eliminated, the 

maximum AC range achievable for the subject would be ~0.104-0.208g/dL. Complete absorption with no 

elimination is not realistic, and the theoretical maximum AC range falls below the measured AC, therefore 

the subject’s drinking history is inconsistent. There was likely alcohol consumption prior to the incident. 

A.5 Minimal case history available

History: Subject is a 25-year-old female, 5’5”, 160 lbs. Crash at 1:00 am, blood draw at 3:00 am, blood 

test result 0.075g/dL. No drinking history available. 

Question: What was her AC at the time of the crash? 

Relevant Information

The subject is 5’5”, 160 lbs

“Standard” drink = 14g of alcohol

Assumptions:

With no drinking history, the impact of potentially unabsorbed alcohol is presented.

Since there is no information on the type of drinks, a standard drink will be used.

Calculations:

Weight conversion: w = 160 lbs × 0.454 kg

lbs = 73 kg

Elapsed Time = 1:00 am to 3:00 am = 2 hours

Using Equation 6 and an elimination rate range of 0.010-0.025 g/dL/hour, calculate the AC at 

time of incident if post absorptive:

ACinc = 0.075 g

dL + (0.010 gdL/hour × 2 hours) = 0.095 gdL

ACinc = ACtest + (R × T)

ACinc = 0.075 g

dL + (0.025 gdL/hour × 2 hours) = 0.125 gdL

Using Equation 5 and a Vd range of 0.40-0.80 L/kg, calculate the maximun AC a “standard” 

drink could contribute:
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

19

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

D

Vd ×w ×10 dL

L

ACdrink(s) =

14g

0.40 L

kg×73kg ×10 dLL

ACdrink(s) =

14g

0.80 L

kg×73kg ×10 dLL

ACdrink(s) = 0.048g/dL ACdrink(s) = 0.024g/dL

Using Equation 7, adjust the AC to remove the number of drinks that would have to be 

unabsorbed to have the subject be below the legal limit at the time of the crash (using the 

calculated ranges of ACinc and ACdrink(s)):

Adjusted ACinc = ACinc – ACdrink(s)

Estimated AC @ 1:00am 0.010 rate 0.025 rate

Post absorptive (ACinc) 0.095 0.095 0.125 0.125

ACdrink(s) (Vd 0.40-0.80) 0.048 0.024 0.048 0.024

-1 drink unabsorbed 0.047 0.071 0.077 0.101

-2 drinks unabsorbed 0.077

Opinion: If the subject was post absorptive at the time of the incident, they were likely above the 0.08g/dL

legal limit at that time. However, if the subject had ~1-2 standard drinks unabsorbed at the time of the 

incident, they could have been below the 0.08g/dL legal limit.
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

20

Annex B Bibliography (informative)

1. Caplan, Y., Goldberger, B. and Aguayo, E. Garriott's medicolegal aspects of alcohol. 6th ed. Lawyers & 

Judges Publication Company, Inc, 2014.

2. Charlton, S.G. and Starkey, N.J. Driver risk from blood alcohol levels between 50mg/100ml and 

80mg/100ml, NZ Transport Agency Research Report 541, 2013. 

3. Cowan, J., Weathermon, A., McCutcheon, J. and Oliver, R. Determination of Volume of Distribution for 

Ethanol in Male and Female Subjects. Journal of Analytical Toxicology, 1996.

4. Evaluation of Breath Alcohol Profiles and Testing the Reliability of Widmark calculations, Amy 

McElroy SDPD 2009

5. Forrest, A. The Estimation of Widmark's Factor. Journal of the Forensic Science Society, 1986.

6. Charlebois, R. et al. Comparison of Ethanol Concentrations in Blood, Serum, and Blood Cells for 

Forensic Application. Journal of Analytical Toxicology, 1996.

7. Ganert, P.M. and Bowthorpe, W.D. Evaluation of Breath Alcohol Profiles Following A Period of Social 

Drinking, Canadian Society of Forensic Science Journal, 2000.

8. Harger, R.N. Blood Source and Alcohol Level; Errors from Using Venous Blood During Active 

Absorption, Alcohol and Road Traffic Proceedings of 3rd International Conference on Alcohol and 

Road Traffic, 1963. 

9. Jakus, J.T. and Shajani, N.K. and Image, B.A. Consumption of a Large Dose of Alcohol in a Short Time 

Span, Forensic Science International, 1992. 

10. Jones, A.W. Disappearance Rate of Ethanol from the Blood of Human Subjects: Implications in Forensic 

Toxicology. Journal of Forensic Sciences, 1993.

11. Jones, A.W. Evidence-based survey of the elimination rates of ethanol from blood. Forensic Science

International, 2010.

12. Jones, A.W. Interindividual Variations in the Disposition and Metabolism of Ethanol in Healthy Men, 

Alcohol, 1984.

13. Jones, A.W. and Andersson, L. Influence of Age, Gender, and Blood-Alcohol Concentration on the 

Disappearance Rate of Alcohol from Blood in Drinking Drivers, Journal of Forensic Sciences, 1996. 

14. Jones, A.W. and Jönsson, K.A. Food-Induced Lowering of Blood-Ethanol Profiles and Increased Rate 

Elimination Immediately After a Meal, Journal of Forensic Sciences, 1994. 

15. Jones, A.W. and Neri, A. Evaluation of Blood-Ethanol Profiles after Consumption of Alcohol Together 

with a Large Meal, Canadian Society of Forensic Science Journal, 1991. 
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

21

16. Jones, A.W. and Wigmore, J.G. and House, C.J. The Course of the Blood-Alcohol Curve After 

Consumption of Large Amounts of Alcohol under Realistic Conditions, Canadian Society of Forensic 

Science Journal, 2006.

17. Kugelberg, F.C., Jones, A.W. Interpreting Results of Ethanol Analysis in Postmortem Specimens: A 

review of the literature. Forensic Science International, 2007.

18. Maudens, K., Patteet, L., van Nuijs, A., Van Broekhoven, C., Covaci, A. and Neels, H. The influence of 

the body mass index (BMI) on the volume of distribution of ethanol. Forensic Science International, 

2014.

19. McElrea, A. and Su, C. and Smith, L. Truncation of Breath Alcohol Measurements and Its Effect on Peak 

Concentrations, Journal of the Canadian Society of Forensic Science, 2011.

20. Montgomery, Mark, Reasor, Mark. Retrograde Extrapolation of Blood Alcohol Data: An Applied 

Approach. Journal of Toxicology and Environmental Health, 1992.

21. Neuteboom, W., Jones, A.W. Disappearance Rate of Alcohol from the Blood of Drunk Drivers 

Calculated from Two Consecutive Samples; What do the Results Really Mean? Forensic Science 

International, 1990.

22. O'Neal, C.L., Poklis, A. Postmortem production of ethanol and factors that influence interpretation: a 

critical review. American Journal of Forensic Medicine and Pathology, 1996. 

23. San Diego Police Department Crime Lab, Alcohol Section Training Studies (pending ToxTalk 

publication), 2006

24. San Diego Sheriff's Regional Crime Laboratory, Alcohol Section Training Studies (pending ToxTalk 

publication), 2012-2018

25. Seidl, S., Jensen, U. and Alt, A. The calculation of blood ethanol concentrations in males and females.

International Journal of Legal Medicine, 2000.

26. Stowell, A.R., Stowell, L.I. Estimation of Blood Alcohol Concentrations After Social Drinking. Journal 

of Forensic Sciences, 1998.

27. UKIAFT 2019. UKIAFT Guidelines for Performing Alcohol Technical Defence Calculations – version 

3.0

28. Ulrich, L., Cramer, Y., Zink, P. Relevance of individual parameters in the calculation of blood alcohol 

levels in relation to the volume of intake | Die Berücksichtigung individueller Parameter bei der 

Errechnung des Blutalkoholgehaltes aus der Trinkmenge., Blutalkohol, 1987.

29. Watson, P., Watson, I. and Batt, R. Prediction of blood alcohol concentrations in human subjects. 

Updating the Widmark Equation. Journal of Studies on Alcohol, 1981.

30. Watkins, Richard L. and Adler, Eugene V. The Effect of Food on Alcohol Absorption and Elimination 

Patterns, Journal of Forensic Sciences, 1993.
2020-S-0003 Guidelines for Performing Alcohol 

Calculations in Forensic Toxicology

22

31. Winek, Charles L. and Wahba, Wagdy W. and Dowdell, Jody L. Determination of Absorption time of 

Ethanol in Social Drinkers, Forensic Science International, 1996

32. Winek, C., Murphy, K. The Rate and Kinetic Order of Ethanol Elimination. Forensic Science 

International, 1984

33. “What Is A Standard Drink?” National Institute on Alcohol Abuse and Alcoholism, U.S. Department of 

Health and Human Services, www.niaaa.nih.gov/alcohol-health/overview-alcoholconsumption/what-standard-drink, 09 Apr. 2018. 

34. Yang, Chi-ting. A study of alcohol pharmacokinetic of local Chinese in Hong Kong, University of Hong 

Kong, 2003.