Blood Alcohol (BAC) Calculator
Estimate blood alcohol concentration from drinks, body weight and time.
Results update as you type.
About this calculator
A blood alcohol content (BAC) calculator estimates the alcohol in your bloodstream using the Widmark formula, from the number of standard drinks, your body weight and sex, and the time since your first drink. It is an educational estimate only — many factors change real BAC, so never use it to decide whether to drive.
Widmark works out grams of alcohol, spreads them through the body water, and subtracts what has already been metabolised: BAC% = alcohol grams ÷ (body-weight grams × r) × 100 − 0.015 × hours, where r is about 0.68 for men and 0.55 for women. For a 75 kg man who has had 3 US standard drinks (3 × 14 = 42 g of alcohol) over 1 hour, that is 42 ÷ (75,000 × 0.68) × 100 − 0.015 = roughly 0.067% — near, but under, the common 0.08% legal limit.
The tool also shows a rough time to sober up, dividing your current BAC by the 0.015% per hour the body clears. That elimination rate is fixed — coffee, water, food and a cold shower do not speed it up. Real BAC depends on drink strength, food, hydration, medication and individual metabolism, so this is for education only: if you have been drinking, do not drive.
Frequently asked questions
What is the Widmark formula?
BAC% = (grams of alcohol ÷ (body-weight grams × r)) × 100 − 0.015 × hours, where r is the distribution ratio (about 0.68 for men and 0.55 for women) and 0.015 is the percent of alcohol eliminated per hour.
Is this accurate enough to decide if I can drive?
No. Real BAC depends on food, hydration, medication, drink strength and individual metabolism, and the estimate can easily be off. If you have been drinking, do not drive — this tool is for education only.
How long until my BAC returns to zero?
The body clears alcohol at roughly 0.015 percent per hour regardless of coffee, water or a cold shower. The calculator divides your current BAC by that rate to estimate the sober-up time.
How many drinks does it take to reach 0.08?
It depends on weight, sex and time. For a 75 kg man, roughly 3–4 standard drinks in an hour can approach 0.08%, but this is only an estimate — never use it to judge whether you are fit to drive.
How long does alcohol stay in your system?
BAC falls at about 0.015% per hour, so a 0.08% level takes roughly five hours to reach zero. Nothing speeds up elimination — not coffee, water, food or a shower.
What counts as one standard drink?
In the US a standard drink is about 14 g of pure alcohol — a 12 oz beer, 5 oz wine or 1.5 oz of spirits. A UK unit is 8 g; set the grams-per-drink field to match your country’s definition.
Why does sex change the estimate?
The Widmark r factor is lower for women (about 0.55 versus 0.68 for men) because of differences in body-water distribution, so the same drinks tend to produce a higher BAC in women.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/bac/curl
curl "https://calculator.free/api/v1/bac/?sex=male&units=metric&weight=75&drinks=3&hours=1"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/bac/?" + new URLSearchParams({
"sex": "male",
"units": "metric",
"weight": "75",
"drinks": "3",
"hours": "1"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.