Blood Alcohol Content Calculator
Get a rough estimate of your blood alcohol content based on weight, gender, number of drinks and time, using the Widmark formula.
How to use the BAC calculator
- Choose your gender and enter your weight.
- Enter the number of standard drinks you've had (1 drink ≈ 1 glass of wine, 1 bottle of beer, or 1 shot of spirits).
- Enter how many hours it's been since you started drinking.
- Choose which legal limit to compare your estimate against. The calculator shows an estimate of your BAC, and whether it's above or below that limit.
How the BAC is calculated
The calculator uses the Widmark formula, a classic method for estimating blood alcohol concentration:
r = 0.68 for men, 0.55 for women — 1 drink ≈ 12 g of pure alcohol
The formula accounts for the fact that alcohol distributes differently in the body depending on gender (the r factor), and that the body breaks down alcohol at a fairly steady rate of around 0.15 ‰ per hour. The result is only a mathematical estimate — actual BAC is also affected by stomach contents, drinking pace and individual differences in metabolism.
Frequently asked questions
How accurate is this calculator?
The Widmark formula gives only a rough estimate. Actual BAC is affected by stomach contents, drinking pace, medication and individual differences, and can therefore deviate from the calculated result in either direction.
Which countries use which legal limit?
0.2 ‰ applies in Norway, Sweden and Poland — among the strictest limits in the world. 0.5 ‰ is the most common limit across the EU, and also applies in Scotland and Australia. 0.8 ‰ applies in England, Wales, Northern Ireland, the United States and Canada. Some countries — including the Czech Republic, Hungary, Romania and Slovakia — have zero tolerance. Many countries also set lower limits for novice or professional drivers, so always check the specific rules where you're driving.
How much is one standard drink?
One standard drink corresponds to roughly 12 grams of pure alcohol — for example a bottle of beer (33 cl, 4.5 %), a glass of wine (12 cl, 12 %) or a shot of spirits (4 cl).