In England, proof is measured by comparing equal volumes of water and the beverage at 51 degrees Fahrenheit. This means that a beverage that is said to be 100 proof under the British system is 114.2 proof under the American system. A beverage that is 100 proof under the American system is said to be 87.6 proof under the British system. The dose of alcohol is calculated by multiplying the volume of an alcoholic beverage by the percentage of alcohol by volume. Absolute alcohol is alcohol without any water molecules in it.
Alcohol produced by distillation contains water molecules that are very hard to remove.
Some typical servings of other alcoholic beverages do NOT contain a single drink equivalent. 0.6 drink equivalents 1.25 ounce shot of 151 proof rum 0.94 oz. One gram of ethyl alcohol yields 7 calories of energy when metabolized by the body. Although most evidentiary rules specify that the proportion of alcohol in the whole blood by used to measure the level of intoxication, most hospitals routinely calculate the proportion of a drug in the plasma portion of the blood. While this measurement is the most useful one for medical purposes, it is not the appropriate one for most legal purposes.