Blood Alcohol Content (BAC) Estimator
Estimate your blood alcohol content (BAC) with the Widmark formula. Enter how many grams of pure alcohol you drank, your body weight, your sex, and how long ago you started, and this calculator returns a rough BAC percentage.
Rates and fees change frequently. Always confirm the current figures
with the official authority before relying on this result.
- Widmark estimate only; real BAC varies widely. Not for legal or driving decisions.
Formula
BAC% = [alcohol (g) ÷ (weight g × r)] × 100 − 0.015 × hours
- The Widmark formula estimates BAC as alcohol mass divided by (body water-adjusted) body mass, minus the alcohol your body has already metabolised.
- r is the Widmark distribution factor: about 0.68 for men and 0.55 for women, reflecting differences in body water.
- The body clears roughly 0.015% BAC per hour, which is why time since your first drink lowers the estimate.
- One standard drink contains about 14 g of pure alcohol; enter the total grams across all drinks.
- This is a rough population estimate only — real BAC varies with food, metabolism, and medication, so never use it to decide whether to drive.
40 g alcohol, 70 kg male, 1 hour
Inputs
- Pure Alcohol Consumed: 40 g
- Body Weight: 70 kg
- Sex: male
- Hours Since Drinking: 1 h
For a 70 kg man (r = 0.68), 40 g of alcohol gives about 0.084% before metabolism. After one hour (−0.015%), the estimated BAC is roughly 0.069%.
Frequently asked questions
What is the Widmark formula?
It is the classic equation for estimating blood alcohol content from the amount of alcohol consumed, body weight, sex, and time elapsed.
How much alcohol is in a standard drink?
About 14 grams of pure alcohol — roughly a 12 oz beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits. Add up the grams across all your drinks.
Why do men and women get different results?
Women generally have a lower proportion of body water, so the same alcohol is less diluted, giving a higher BAC. The formula uses a different r factor for each.
How fast does BAC drop?
Roughly 0.015% per hour on average, but this varies between people. The calculator subtracts that rate based on the time since your first drink.
Can I use this to decide if I can drive?
No. This is only a rough estimate and can be badly off for any individual. Never rely on it for driving or legal decisions.
Related calculators
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