Blood Alcohol Content (BAC) Estimator
Estimate blood alcohol content from body weight, sex, standard drinks consumed and hours elapsed, using the Widmark formula. A rough educational estimate only — never a substitute for a breathalyzer, and never a basis for deciding whether to drive.
Input
Used for the Widmark distribution ratio (r ≈ 0.68 for men, 0.55 for women).
1 US standard drink = 14 g pure alcohol ≈ 12 oz beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%).
The body metabolizes roughly 0.015% BAC per hour.
Output
| Metric | Value |
|---|---|
| No data yet | |
<strong>Educational estimate only — not a medical or legal tool.</strong> This calculator uses the Widmark formula with average absorption and metabolism assumptions. Actual BAC varies widely with food intake, hydration, medication, genetics, liver function, and the pace of drinking, and can differ significantly from this estimate. It cannot tell you whether you are legally fit to drive. <strong>Never use this tool to decide whether to drive — if you have been drinking, do not drive.</strong> Use a rideshare, taxi, or designated driver instead.
Guides
This calculator gives a rough estimate of your blood alcohol content (BAC) based on body weight, biological sex, the number of standard drinks you've had, and how many hours have passed since your first drink. It uses the Widmark formula, the same method behind most consumer BAC calculators and breathalyzer-education charts. It is built for education and curiosity — not for deciding whether it's safe to drive.
How it works: the Widmark formula
The Widmark formula estimates BAC as:
BAC% = (alcohol grams consumed / (body weight in grams × r)) × 100 − (metabolism rate × hours elapsed)
- Alcohol grams comes from the number of standard drinks you enter, multiplied by 14 g — the US definition of one standard drink (about 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits). Some countries define a standard drink differently (10 g in the UK and Australia), so if you're used to a different convention, adjust the drink count accordingly.
- r is the Widmark distribution ratio, which accounts for how alcohol spreads through body water: roughly 0.68 for men and 0.55 for women, reflecting typical differences in body composition. This is a population average, not a measurement of you specifically.
- Metabolism rate is fixed at about 0.015% BAC per hour, the commonly cited average rate at which the liver clears alcohol. The result is clamped at a minimum of 0.000%, since metabolism can't push BAC below zero.
The tool also estimates how long until you're back under the US legal driving limit of 0.08% and how long until you're back to 0.00%, purely as a projection of the same formula forward in time.
How to use it
- Select your biological sex — this sets the Widmark distribution ratio used in the formula.
- Enter your body weight and choose kilograms or pounds.
- Enter the number of standard drinks you've consumed (14 g of pure alcohol each, US convention).
- Enter how many hours have passed since your first drink.
- The estimated BAC, status, and legal-limit comparison update automatically.
Why this is only a rough estimate
The Widmark formula was developed decades ago from population averages, and real BAC depends on far more than weight and drink count: how much food is in your stomach, how fast you drank, hydration, medication, liver health, genetics, and individual metabolism can all shift your actual BAC well away from this estimate — in either direction. Two people with identical inputs can have meaningfully different true BAC.
Safety and legal disclaimer
This tool is for educational purposes only. It is not a breathalyzer, a medical device, or a legal determination of fitness to drive, and it must never be used to decide whether you (or anyone else) is safe to get behind the wheel. Impairment can begin well below the legal limit, and the legal limit itself varies by jurisdiction and by driver class (e.g., commercial or under-21 drivers face lower limits). If you have been drinking at all, the only safe choice is not to drive — call a rideshare, a taxi, or a sober friend, or stay where you are until you're certain you're sober.
Privacy
All calculations run entirely in your browser. Nothing you enter — weight, sex, drink count, or timing — is sent to a server or stored.