Blood Alcohol Content Calculator

Estimated blood alcohol content is a mass balance question: how much ethanol is in how much water.

Standard drinksCount standard drinks of fourteen grams of ethanol, not glasses.Body weightBody weight in the unit selected below.Weight unitThe formula needs kilograms. Pounds are converted automatically.Body water fractionShare of body mass that is water. The main source of variation between people.Hours since the first drinkHours elapsed, used to subtract the metabolised amount.

Estimated blood alcohol content

0.0582

Peak content before metabolism: 0.0882
Hours until the estimate reaches zero: 3.8824

Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.

The formula this calculator uses

BAC = (standard drinks x 14) / (r x body weight in kg x 10) - 0.015 x hours

BAC: Estimated blood alcohol content, grams per decilitre
drinks: Number of standard drinks, 14 grams of ethanol each
r: Body water fraction, about 0.68 for men and 0.55 for women
hours: Hours since the first drink

How to check the result by hand

1
Count standard drinks, not glasses
Fourteen grams of ethanol each. A five ounce pour of twelve percent wine is one, a sixteen ounce pint of five percent beer is closer to two, and a large home measure of spirits can be more.
2
Convert body weight to kilograms
Pounds times 0.4536 gives kilograms. A one hundred and ninety pound man is about eighty six kilograms, and the formula needs kilograms to match the litre-based water volume.
3
Pick the body water fraction
Use 0.68 for an average man and 0.55 for an average woman. This is the empirical correction for body composition, and it is the largest single source of variation between people.
4
Divide ethanol mass by the water volume
Forty two grams over four hundred and seventy six decilitres is 0.0882. Multiplying body mass by the water fraction and by ten converts kilograms of water into decilitres.
5
Subtract the metabolised amount
Two hours at 0.015 an hour is 0.03, leaving 0.0582. This is the estimate at that moment, and only time will reduce it further.

For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Blood Alcohol Content page.