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About this tool
Estimate BAC from standard drinks using the Widmark formula. For education only.
The Blood Alcohol Content Calculator estimates BAC with the Widmark formula, treating each standard drink as 14 grams of pure alcohol, dividing by body weight times a distribution factor of 0.68 for men or 0.55 for women, and subtracting 0.015 percentage points per hour for elimination. It reports the result as a percentage and flags whether it sits above or below the 0.08% threshold used in most of the United States. It is an educational estimate for understanding how drinks, weight and time interact — never a fitness-to-drive test.
Open Blood Alcohol Content Calculator on AltFTool — it loads instantly in your browser.
Enter how many drinks you have had in the 'Standard drinks' field, which starts at 3; each one is counted as 14 g of alcohol and totalled in the 'Alcohol consumed' box under the result.
Enter your weight in the 'Body weight (kg)' field (default 70) and pick 'Male' or 'Female' under 'Sex' — the Widmark distribution ratio used is 0.68 for male and 0.55 for female.
Set 'Hours since first drink' to subtract 0.015% per hour, reported as 'Approx. burned off'. The estimate updates live with no button to press, reading '0.058% BAC' and 'Under 0.08%' at the defaults, or 'Over the common 0.08% legal limit' above that — the page's own note warns it is an estimate only, never a decision about driving.
The 14 g standard drink, the 0.68 and 0.55 distribution factors and the 0.015 per hour elimination rate are the Widmark constants, not hidden fudge factors.
Seeing that three drinks is 42 grams of ethanol makes the input side of the calculation concrete and easy to sanity-check.
Hours since the first drink are subtracted at the elimination rate, so the estimate falls as it should rather than treating all drinks as if consumed at once.
The Widmark equation: grams of alcohol divided by (body weight in grams x the distribution factor r), expressed as a percentage, minus 0.015 per hour elapsed. Here r is 0.68 for men and 0.55 for women, reflecting differences in body water proportion.
This tool uses 14 grams of pure ethanol, the US standard drink — roughly a 350 ml regular beer at 5%, 150 ml of wine at 12%, or 45 ml of 40% spirits. The UK unit is 8 grams and Australia uses 10, so convert before entering a count.
Roughly one hour per standard drink, since the body clears alcohol at about 0.015 percentage points of BAC per hour and one drink raises a typical adult by around that much. A BAC of 0.08% therefore takes about five hours to reach zero — and nothing speeds it up: not coffee, food, a cold shower or exercise.
No. This is an educational estimate only. Real BAC varies with food, medication, drinking pace, health and individual metabolism, and impairment begins well below any legal limit — 0.05% in much of Europe and 0.03% or effectively zero in India, Brazil and many other countries. If you have been drinking, do not drive.
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