BAC Calculator
Enter your body weight, sex, the number of standard drinks and the hours since your first drink. The calculator estimates your blood alcohol content (BAC), gives it a status label and shows how many hours it takes to fall to zero at 0.015% an hour. It is an estimate for information only. Never drink and drive.
How to use the BAC Calculator
- Enter your numbers in the BAC Calculator above.
- Press the Estimate BAC button to see the result.
- To try other numbers, change any value and press the button again.
The Widmark BAC formula
BAC % = (A / (W × r)) × 100 − (0.015 × t)
A is total alcohol in grams (drinks × 14 g per standard drink). W is body weight in grams: pounds × 453.59237, or kilograms × 1,000. r is the distribution ratio (0.73 men, 0.66 women). t is hours since the first drink. The result is in percent, rounded to three decimals, and never goes below 0. Hours to sober divides that BAC by 0.015.
Worked example
A 180 lb man having 4 standard drinks over 2 hours: A = 4 × 14 = 56 g. W = 180 × 453.59237 = 81,646.63 g. BAC = (56 / (81,646.63 × 0.73)) × 100 − (0.015 × 2) = 0.094 − 0.030 = 0.064%. That is under the 0.08% limit most US states use, and the calculator labels it "Moderately impaired". It shows 4.3 hours to sober, because 0.064 ÷ 0.015 is about 4.3.
Frequently asked questions
What is the legal driving limit?
In the US: 0.08% BAC for adults (0.05% in Utah). In most of Europe: 0.05%. For commercial drivers (US): 0.04%. Under 21 zero-tolerance laws apply in all US states.
How quickly does BAC decrease?
The calculator takes 0.015% off for every hour since your first drink, and its hours to sober figure uses that same rate. Real bodies clear alcohol at different rates, and the calculator cannot see yours.
What do the status labels mean?
They follow the BAC the calculator prints. A BAC of 0% reads Sober, below 0.04% Slightly impaired, below 0.08% Moderately impaired, below 0.15% Significantly impaired, and 0.15% or more Severely impaired. The labels are the calculator's own bands, not a legal or medical test.
How accurate is this estimate?
It is a rough estimate. The formula knows your weight, sex, drink count and hours. It assumes 14 g of alcohol in every drink and the same elimination rate for everyone. Your real BAC also depends on food, hydration, medication, liver function and how strong each drink was, and the calculator sees none of that. Never rely on calculations to decide whether to drive.