How is blood alcohol concentration (BAC) estimated?

The classic Widmark formula divides the grams of alcohol consumed by body mass in grams multiplied by a body-water distribution ratio (about 0.68 for males and 0.55 for females), then multiplies by 100 to express the result as a percentage. The body then eliminates alcohol at a roughly constant rate of about 0.015% per hour.

How long does it take to metabolize one standard drink?

A US standard drink contains about 14 grams of pure ethanol — roughly a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot at 40%. Most adults clear about one standard drink per hour, but the true rate varies from roughly 0.012 to 0.020% BAC per hour depending on genetics, liver health, and other factors.

Can a BAC calculator tell me when it is safe to drive?

No. Calculators like this use population averages, and real BAC varies enormously between individuals and even day to day. Food, medications, hydration, and genetics all shift the result. Never use an estimate to decide whether you can drive — if you have been drinking, do not drive.

Alcohol Metabolism Calculator

Your night

Sex

Sets the Widmark body-water ratio (0.68 / 0.55).

Units

Body weight

lbs

Standard drinks

drinks

1 US standard drink = 14 g ethanol ≈ 12 oz beer (5%) · 5 oz wine (12%) · 1.5 oz shot (40%).

Time of first drinkUsed to project the "sober by" clock time.

Estimated peak BAC

— %

Peak BAC (Widmark)—

Below 0.08% (US legal limit) in—

Back to ~0.00% in—

At peak you'd likely feel—

Estimated BAC decline

Assumes an average elimination rate β of 0.015% per hour (real-world range ≈ 0.012–0.020) and that all drinks are absorbed. Drinking over several hours flattens the true peak.

How this works

Methodology reviewed July 2026

The tool estimates peak blood-alcohol concentration and when it returns toward zero using the Widmark equation — the standard model relating alcohol consumed, body water, and the body's steady elimination rate. It is an educational timeline of how alcohol clears, nothing more.

Formula

BAC (%) = (alcohol in grams / (body weight in g × r)) × 100 − (β × hours)
  r ≈ 0.68 (men), 0.55 (women)   ·   β ≈ 0.015 %/hour
  one standard drink ≈ 14 g alcohol

Inputs

Sex · Body weight · Drinks and their timing

Outputs

Estimated peak BAC · Approximate time BAC returns to ~0

Assumptions

Widmark uses population-average body-water and elimination constants.
Assumes typical absorption; food, drink strength, and timing all shift the real curve.

Limitations

Individual elimination varies widely with genetics, food, medications, and liver health.
The model can't know your true absorption on a given night.

Safety

This is an educational estimate and NEVER a fitness-to-drive or fitness-to-work test. Do not use it to decide whether it is safe or legal to drive — it isn't designed for that and can be wrong in either direction.
The only sure way to know you're unimpaired is not to have been drinking.

This calculator is for educational purposes only and is not medical advice, diagnosis, or treatment. Results are estimates based on published formulas and population averages — your individual values may differ. Nothing here is calculated on a server: everything runs in your browser and no data is stored or sent anywhere. Always consult a qualified clinician before making health, medication, or training decisions.