Standard drink

A standard drink or (in the UK) unit of alcohol is a measure of alcohol consumption representing a fixed amount of pure alcohol. The notion is used in relation to recommendations about alcohol consumption and its relative risks to health. It helps to inform alcohol users.
A hypothetical alcoholic beverage sized to one standard drink varies in volume depending on the alcohol concentration of the beverage (for example, a standard drink of spirits takes up much less space than a standard drink of beer), but it always contains the same amount of alcohol and therefore produces the same amount of intoxication. Many government health guidelines specify low to high risk amounts in units of grams of pure alcohol per day, week, or single occasion. These government guidelines often illustrate these amounts as standard drinks of various beverages, with their serving sizes indicated. Although used for the same purpose, the definition of a standard drink varies from country to country.
Labeling beverages with the equivalent number of standard drinks is common in some countries.
The definition of what constitutes a standard drink varies very widely between countries, with what each country defines as the amount of pure alcohol in a standard drink ranging from 8 to 20 grams.
The sample questionnaire form for the World Health Organization's Alcohol Use Disorders Identification Test (AUDIT) uses 10 g (0.35 oz), and this definition has been adopted by more countries than any other amount. Some countries choose to base the definition on mass of alcohol (in grams) while others base the unit on the volume (in ml or other volume units). For comparison, both measurements are shown here, as well as the number of standard drinks contained in 500 millilitres (16.9 US fluid ounces) of 5% ABV beer (a typical large size of beer in Europe, slightly larger than a US pint of 473 mL). The terminology for the unit also varies, as shown in the Notes column.
It is possible to calculate the pure alcohol mass in a serving from the concentration, density of alcohol, and volume: volume × alcohol by volume × density of alcohol = Pure alcohol mass {\displaystyle {\text{volume}}\times {\text{alcohol by volume}}\times {\text{density of alcohol}}={\text{Pure alcohol mass}}}
For example, a 355 ml (12.0 US fl oz) glass of beer with an ABV of 5.5% contains 19.525 ml of pure alcohol, which has a density of 0.78945 g/mL (at 20 °C), and therefore a mass of 15.41 grams (0.544 oz). 355 m L × 0.055 × 0.78945 g / m L ≈ 15.41 g {\displaystyle 355\,\mathrm {mL} \times 0.055\times 0.78945\,\mathrm {g} /\mathrm {mL} \approx 15.41\,\mathrm {g} } or 0.355 L × 0.055 × 789.45 g / L ≈ 15.41 g {\displaystyle 0.355\,\mathrm {L} \times 0.055\times 789.45\,\mathrm {g} /\mathrm {L} \approx 15.41\,\mathrm {g} }
When the drink size is in fluid ounces (which differ between the UK and the US), the following conversions can be used:
One should bear in mind that a pint in the UK is 20 imperial fluid ounces, whereas a pint in the US is 16 US fluid ounces, and that 1 imperial fl. oz. ≈ 0.96076 US fl. oz.: this means that 1 imperial pint ≈ 1.20095 US pints.
Calculating alcoholic content in countries that use units of alcohol is straightforward, as the volume multiplied by the Alcohol by volume (ABV) gives the alcohol content. In the UK, one unit of alcohol equals one percentage point per litre, of any alcoholic beverage.
volume (in litres) × alcohol by volume (ABV) = alcohol content (units of alcohol) {\displaystyle {\text{volume (in litres)}}\times {\text{alcohol by volume (ABV)}}={\text{alcohol content (units of alcohol)}}}
The standard UK units of alcohol in a drink can be determined by multiplying the volume of the drink (expressed in litres) by its percentage ABV. For example, a standard 750 millilitres (25 US fl oz) bottle of wine at 12% ABV contains:
One UK standard measure of spirits (25ml, 0.025 L) at 40% ABV contains:
One imperial pint (568ml, 0.568 L) of beer at 4% ABV contains:
In the UK, both volume and ABV are usually given on bottles, drinks menus and so on, and so are easy to retrieve.
A standard drink is often different from a normal serving in the country in which it is served. For example, in the United States, a standard drink is defined as 0.6 US fluid ounces (18 ml) of ethanol per serving, which is about 14 grams of alcohol. This corresponds to a 12-US-fluid-ounce (350 ml) can of 5% beer, a 5-US-fluid-ounce (150 ml) glass of 12% ABV (alcohol by volume) wine, or a 1.5-US-fluid-ounce (44 ml) so-called "shot" of spirit, assuming that beer is 5% ABV, wine is 12% ABV, and spirits is 40% ABV (80 proof). Most wine today is higher than 12% ABV (the average ABV in Napa Valley in 1971 was 12.5%), hence will be more than a standard drink. Similarly, although 40% ABV is standard for spirits, the amount of spirit in a mixed drink varies widely.
Most spirits sold in the United Kingdom have 35%-40% ABV. In England, a single pub measure (25 ml (0.85 US fl oz)) of a spirit contains one unit. However, a larger 35 ml (1.2 US fl oz) measure is increasingly used (and in particular is standard in Northern Ireland), which contains 1.4 units of alcohol at 40% ABV. Sellers of spirits by the glass must state the capacity of their standard measure in ml.
In Australia, a 30 ml (1.0 US fl oz) shot of spirits (40% ABV) is 0.95 standard drinks.
In the US, one shot of 80 proof liquor is 1.5 US fl oz (44 ml), which is one US standard drink.
From 1992 to 1995, the UK government advised that men should drink no more than 21 units per week, and women no more than 14. (The difference between the sexes was due to the typically lower weight and water-to-body-mass ratio of women). The Times claimed in October 2007 that these limits had been "plucked out of the air" and had no scientific basis.
This was changed after a government study showed that many people were in effect "saving up" their units and using them at the end of the week, a form of binge drinking. Since 1995 the advice was that regular consumption of 3–4 units a day for men, or 2–3 units a day for women, would not pose significant health risks, but that consistently drinking four or more units a day (men), or three or more units a day (women), is not advisable.
An international study of about 6,000 men and 11,000 women for a total of 75,000 person-years found that people who reported that they drank more than a threshold value of 2 units of alcohol a day had a higher risk of fractures than non-drinkers. For example, those who drank over 3 units a day had nearly twice the risk of a hip fracture.
As a rough guide, it takes about one hour for the body to metabolise (break down) one UK unit of alcohol, 10 ml (8 grams). However, this will vary with body weight, sex, age, personal metabolic rate, recent food intake, the type and strength of the alcohol, and medications taken. Alcohol may be metabolised more slowly if liver function is impaired. For other countries, it may be easiest to convert to UK units. For example, in the United States one standard drink contains 14 grams ≈ 1.75 units of alcohol, and so a US standard drink takes the body about an hour and three-quarters to process. Blood alcohol content can more accurately be estimated by using Widmark's formula.
Australia introduced standard drink labelling in the 1990s, and New Zealand followed with a labelling requirement starting in 2002. The labels were criticized for being too small to read. A focus group study found that most student drinkers used the labels to choose stronger drinks and identify the cheapest method of getting drunk, rather than to drink safely.
In the UK in March 2011, alcohol companies voluntarily pledged to the UK Department of Health to implement a health labelling scheme to provide more information about responsible drinking on alcohol labels and containers. The pledge stated:
At the end of 2014, 101 companies had committed to the pledge labelling scheme.
There are five elements included within the overall labelling scheme, the first three being mandatory, and the last two optional:
Drinks companies had pledged to display the three mandatory items on 80% of drinks containers on shelves in the UK off-trade by the end of December 2013. A report published in November 2014, confirmed that UK drinks producers had delivered on that pledge with a 79.3% compliance with the pledge elements as measured by products on shelf. Compared with labels from 2008 on a like-for-like basis, information on Unit alcohol content had increased by 46%; 91% of products displayed alcohol and pregnancy warnings (18% in 2008); and 75% showed the Chief Medical Officers' lower risk daily guidelines (6% in 2008).
Studies published in 2021 in the UK showed that the label could be further enhanced by including pictures of units and a statement of the drinking guidelines - this would help people understand the recommended limits better.