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Alcohol Doses, Measurements, and Blood Alcohol Levels

The punchline to an often told joke suggests that the reason medical journals use technical jargon is to make sure that only doctors understand the message. With regard to recent medical journal discussions of alcoholic beverage doses and blood alcohol levels, however, a not-so-funny result of the latest extreme in technical jargon is that even doctors often don’t understand the message. In an attempt to develop an “international standard” for measurements described in scientific publications, the so-called Systeme Internationale requires that journals describe doses of beverage alcohol in terms of “grams,” rather than “ounces,” and the blood levels are described in terms of “millimoles per liter,” instead of the usual “percent of alcohol by volume” measurement.

This means that, instead of describing the ingestion of two, twelve ounce beers containing one ounce of absolute alcohol, the medical journal speaks about ingestion of 28.5 grams alcohol. Instead of describing the level of alcohol in a patient’s blood as 0.10% (or 100 mg/dL) the level is described as 22 mmol/L! This system certainly is confusing for the layperson, and is likely to create comprehension problems for many physicians as well.

A “millimole” is one one-thousandth of a “mole.” A “mole” is defined as the amount of a substance contained in exactly 6.02 x 1023 [NOTE: This number is and should be reading as “ten to the twenty-third power.”] molecules of a substance (6.02 x 1023 is called “Avogadro’s number,” and is the number of atoms in 12 grams of pure Carbon). What that has to do with a person’s level of intoxication is beyond most people’s comprehension. Any physician whose mind makes such a logical connection is likely to be unable to communicate on a level his or her patients can understand. Anyone who orders drinks by the gram will probably be presumed to be intoxicated and refused service!

Add to this discussion the differences between measures of the percentage of alcohol “by volume” versus “by weight,” different systems of measuring the “proof” of an alcoholic beverage, medical versus legal standards for measuring blood alcohol levels, and discussions of calorie content and specific gravity. If you are confused, you are not alone. 

Alcohol Doses

Further complicating discussions of amounts of alcohol is the difference between potency measures based upon “percent of alcohol by  volume” and measures based upon “percent of alcohol  by weight.” Since alcohol weighs less than water, any discussion  about the proportion of alcohol in a beverage must specify whether  the comparison is “by weight” or “by volume.”  A pint of water weights about one pound (16 ounces). A pint of  pure alcohol weighs about 12.8 ounces. If one pint of pure alcohol  is mixed with one pint of water, the result is a beverage that  is 50% alcohol “by volume.” If one pound of pure alcohol  is mixed with one pound of pure water, the result is a beverage  that is 50% alcohol “by weight.” Since one pound of  water 16 fluid ounces, and one pound of alcohol is about 20 fluid  ounces, the 36 total fluid ounces in a resulting beverage is about  55.5% alcohol “by volume,” although it is 50% “by  weight.” As an example of the importance of specifying the  system used to measure the percentage of alcohol in a beverage,  Coors Brewing Company promotional materials describe “Zima”  as containing 3.7% alcohol by weight; 4.6% alcohol by volume.  To convert measures by weight into measures by volume (or visa  versa), use a conversion factor of 0.79. 

Measures  of Potency; “Proof”

The  strength of an alcoholic beverage is usually expressed as either  the percentage of absolute alcohol by volume, or as “proof.”  In the USA, proof is a measure of the amount of absolute alcohol  in distilled spirits, and is calculated as the number of parts  of alcohol in 200 parts of beverage at 60 degrees Fahrenheit (a  beverage that is 50% alcohol is “100 proof;” a beverage  that is 43% alcohol is “86 proof”). Under the American  system, one “proof” is equal to one-half percent of  alcohol by volume. 

The  concept of “proof” emerged prior to the 18th century,  when few people had the equipment necessary to make precise measurements  of the percentage of alcohol in a beverage. Exotic formulas, such  as igniting a mixture of equal parts of the beverage and gunpowder,  were used to test the proof of distilled spirits. 

A  different system for measuring proof is used in England, In England,  proof is measured by comparing equal volumes of water and the  beverage at 51 degrees Fahrenheit. 100 proof is set at the point  at which the beverage weighs 12/13th as much as water. 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. 

Alcohol  Doses

The  dose of alcohol is calculated by multiplying the volume  of an alcoholic beverage by the percentage of alcohol by volume.  For example, twelve ounces of beer that is 4% alcohol by volume  would have a dose of 0.48 ounces of alcohol. Pure alcohol (100%  alcohol) is called “absolute alcohol.” Absolute alcohol is alcohol without any water molecules in it. Alcohol produced by distillation contains water molecules that are very hard to  remove. The strongest readily available alcoholic beverage, often called “neutral grain spirits” is about 95% absolute  alcohol (190 proof). It is possible to manufacture absolute alcohol,  also called “scientific alcohol,” by synthesis. 

The  dose of alcohol in a typical 12 ounce can of beer, is approximately  equal to the dose of alcohol in a 4 to 5 ounce serving of wine,  or in a “shot” of whiskey. This average-sized dose of  alcohol is equal to one-half ounce of absolute alcohol, and is  sometimes called a “drink equivalent.” 

 Some  typical servings of other alcoholic beverages do NOT  contain a single drink equivalent. They may contain more or less  alcohol than is found in an “average-sized” dose of alcohol.  Examples include:  


Examples  of Drink Non-Equivalence

Dose  of Alcoholic Beverage

Amount  of absolute alcohol

Number  of drink equivalents

40  ounce bottle of 8% malt liquor

3.2  oz.

6.4  drink equivalents

12  ounce bottle of 2.5% low alcohol beer

0.3  oz.

0.6  drink equivalents

1.25  ounce shot of 151 proof rum

0.94  oz.

1.9  drink equivalents

12.5  ounce bottle of 20% fortified wine cooler

2.5  oz.

5.0  drink equivalents

Alcohol Measurements

Measurements  and Equivalents

One  fluid ounce (U.S.) of alcohol equals:

  •   1.805  cubic inches 
  •   29.573  milliliters 
  •   1.041  British fluid ounces 
  •   and  weighs 0.79 ounces avoirdupois

Common Measurements Of Alcoholic Beverages (U.S.):           _____________________________________________          

Common  Measurements for Alcoholic Beverages

“pony  shot”

0.5  jigger; 0.75 fluid ounces


0.666  jigger; 1 fluid ounce

“large  shot”

1.25  ounces


1.5  shots; 1.5 fluid ounces


16  shots; 0.625 fifths


25.6  shots; 25.6 ounces; 1.6 pints; 0.8 quarts; 0.75706 liters


32  shots; 32 ounces; 1.25 fifths


2  quarts; 2.49797 wine bottles

bottle  wine

0.800633  quarts; 0.7577 liters

Calorie Content of Alcoholic Beverages

One gram of ethyl  alcohol yields 7 calories of energy when metabolized by the body.  That converts of approximately 200 calories per ounce of absolute  alcohol, or about 100 calories per drink equivalent (one-half ounce  of absolute alcohol). The total calorie content of an alcoholic  beverage includes the calories from the alcohol itself, and calories  from other components of the beverage (residual sugars or grains  in beers and wines, for example). A typical serving of regular beer  yields about 150 calories (about 100 calories from the alcohol and  about 50 calories from the residual carbohydrates). A typical serving  of light beer has a lower alcohol content and less residual carbohydrates,  so the total calorie content could be about 100 calories (about  80 calories from the alcohol and about 20 calories from the residual  carbohydrates). 


Conversion Factors for Alternative Measurements

The  most common system for measuring and reporting Blood Alcohol Levels  (BAL) is calculated using the weight of alcohol (milligrams) and  the volume of blood (deciliter). This yields a Blood Alcohol Concentration  that can be expressed as a percentage (ie. 0.10% alcohol by volume),  or as a proportion (ie. 100 mg. per deciliter). This system is  the one prescribed by almost every state, and is sometimes referred  to as the “weight by volume” or “w/v” method. 

A  few states prescribe a “weight by weight” or “w/w”  method (milligrams of alcohol in milligrams of blood). For forensic  evidence purposes, the w/w can be calculated by dividing the w/v  by a factor or 1.055 (the average specific gravity of blood). 

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. Since the addition of red and white  blood cells would add to the blood volume that dilutes the alcohol,  using only the plasma fraction would result in a percentage of  alcohol that is higher than would be found in whole blood. Although  there is some variation from person to person, depending upon  the density of their bloods, the average adjustment factor is  1.16. In other words, to estimate the alcohol level in whole blood  using the alcohol level in blood plasma, divide by 1.16. For example,  a plasma alcohol level of 0.15% would convert to a blood alcohol  level of 0.13%.   

Comparison  of Blood Alcohol Level Reporting Systems
Six  different methods of reporting the same blood alcohol  measurement.
Method  of Stating the Measurement Result
Blood  Alcohol Concentration (percent weight to volume) 0.10%
Milligrams  per milliliter 1.0
Milligram  percent (milligrams per 100 ml.) 100
parts  per million 1000
Percent  by weight (weight by weight)

For Even more information about Alcohol and the Human Body please click on the following links:

For a Blood Alcohol Calculator click here

Other Articles of Interest:

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H. Michael Steinberg Esq.
Attorney and Counselor at Law
The Colorado Criminal Defense Law Firm of H. Michael Steinberg
A Denver, Colorado Lawyer Focused Exclusively On
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