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How blood alcohol concentration is estimated
Blood alcohol concentration is the percentage of alcohol in your bloodstream. This calculator uses the Widmark formula, the same model behind most published BAC tables, taking your weight, sex, how much you drank, its strength and how long ago you started. The result is an estimate only — real BAC varies with food, medication, hydration and individual metabolism.
How to use the Blood Alcohol Calculator
- Enter your Weight (kg) and Gender.
- Enter the total Volume (ml) of drink consumed.
- Enter the Alcohol content (%) — around 5% for beer, 12% for wine, 40% for spirits.
- Enter Hours since first drink; your body clears roughly 0.015% per hour.
Formula and a worked example
BAC = (A ÷ (r × W)) × 100 − (0.015 × hours)
A is grams of pure alcohol, W is body weight in grams, and r is the Widmark distribution factor — about 0.68 for men and 0.55 for women, reflecting differences in body water. Pure alcohol grams are volume × strength × 0.789.
Worked example
A 70 kg man drinking 500 ml of 5% beer consumes about 19.7 g of alcohol. One hour after starting, his estimated BAC is roughly 0.026% — well under the common 0.08% limit, but the same drink in a 55 kg woman gives about 0.041%.
Frequently asked questions
Can I use this to decide whether to drive?
No. Never use any calculator to judge fitness to drive. Individual variation is large, the model ignores food and medication, and legal limits differ by country. If you have been drinking, do not drive.
Why do men and women get different results?
Body water differs. Alcohol distributes through water, so at the same weight a woman typically reaches a higher concentration from the same drink.
How fast does alcohol leave the body?
About 0.015% BAC per hour, and it cannot be accelerated. Coffee, cold showers and food after the fact make no difference to the rate.
Does food change my BAC?
Eating slows absorption so the peak is lower and later, but it does not reduce the total alcohol your body must process.
Related calculators
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