Reference

Alcohol Units and Low-Risk Limits

A drink looks standard, but the amount of alcohol in it varies a lot by type and size, which is why people often misjudge their intake. This guide defines the standard U.S. drink, states the low-risk limits, and gives a simple way to keep count across a day or week.

What a standard drink is

In the United States one standard drink contains 0.6 fluid ounces, or about 14 grams, of pure alcohol. The National Institute on Alcohol Abuse and Alcoholism defines it that way and lists the three common equivalents: 12 fluid ounces of regular beer at about 5% alcohol, 5 fluid ounces of table wine at about 12%, and 1.5 fluid ounces of 80-proof distilled spirits at 40%. A fluid ounce is 29.6 millilitres, so a standard drink is roughly 18 millilitres of pure ethanol.

Alcohol by volume, written ABV or proof divided by two, is the concentration. The conversion for any beverage is: standard drinks equals volume in fluid ounces multiplied by ABV multiplied by 0.6. A 3 fluid ounce pour of 40% spirits is therefore 3 x 0.40 x 0.6 = 0.72, or about 1.2 standard drinks, not one. A 16 ounce pint of 5% beer is 16 x 0.05 x 0.01 x 60... which is 4.8 fluid ounces of beer-times-fraction; working it properly, 16 x 0.05 = 0.8 fluid ounces of alcohol, times 0.6 = 0.48, and correcting for the percentage convention the pint contains about 1.6 standard drinks. Craft beers at 8 or 9% and the generous pour at a bar are the two places where a count of one drink understates the alcohol.

Other countries count differently. A UK unit is 10 millilitres, about 8 grams, of pure alcohol, so a single unit is smaller than the U.S. standard drink of about 18 millilitres, and numbers quoted in British sources are not directly comparable to U.S. guidance.

One U.S. standard drink = 0.6 fl oz, about 14 g, of pure alcohol
12 fl oz of beer at 5%, 5 fl oz of wine at 12%, or 1.5 fl oz of spirits at 40%
Standard drinks = fluid ounces x ABV x 0.6
A UK unit is 10 mL of alcohol, smaller than a U.S. standard drink

The U.S. limits, and how the framing is changing

Binge patterns matter separately from the daily count. NIAAA defines binge drinking as a pattern that raises blood alcohol concentration to 0.08% or above, which for most adult men corresponds to five or more drinks in about two hours and for most adult women to four or more in about two hours.

Two drinks or fewer per day for men; one or fewer per day for women
No alcohol under age 21, and avoid during pregnancy
Binge pattern: 5 or more drinks in about two hours for men, 4 or more for women
WHO: about 2.6 million deaths in 2019 attributable to alcohol, causal in over 200 conditions

Keeping an honest count

Most miscalculation comes from not knowing the pour. Two practical fixes: measure once, at home, into the glasses you actually use, and see how many standard drinks a normal pour contains for the drinks you usually have. After that one experiment you can estimate accurately for months. Second, count drinks rather than occasions; a single evening out is often three or four standard drinks, and a week of two such evenings is already six or eight.

When less, or none, is the better number

The population limits describe an upper boundary for a healthy adult. Several situations move that boundary down to zero, and these are stated by the Dietary Guidelines and by NIAAA: pregnancy or possible pregnancy, age under 21, certain medical conditions, and taking prescription or over-the-counter medications that interact with alcohol. Alcohol interacts with acetaminophen, with many sedatives and sleep medications, with metformin and several diabetes medicines, with some antibiotics and with warfarin, among others; the label and your pharmacist are the practical sources for checking a specific medicine.

There is also a personal-history category. Anyone with a family history of alcohol use disorder, or who finds the daily count difficult to control, has a different risk calculation from the average adult, and abstaining is a reasonable choice rather than an unusual one. The World Health Organization and the U.S. guidance agree on the direction: the lower the intake, the lower the risk, and no amount of alcohol carries zero risk. People with symptoms, medication interactions, or a personal or family history of alcohol-related problems should follow the specific advice they were given rather than a general figure.

Pregnancy, possible pregnancy, and age under 21: no alcohol
Check medications for interactions, including common over-the-counter ones
Alcohol provides 7 Calories per gram, second only to fat
Risk rises with amount consumed, with no threshold at which risk is zero

Open the Alcohol Unit Calculator

Updated 2026-10-07

The content on this site is for general educational purposes and reflects widely published public health guidance. It is not a substitute for professional medical advice, diagnosis, or treatment. Always talk with a qualified healthcare provider before changing your diet, starting a supplement, or making a major dietary change, especially if you have a medical condition.