Blood Alcohol Calculator
This calculator estimates blood alcohol concentration with the Widmark formula, from drinks consumed, bodyweight, sex and elapsed time. Treat every result as a rough guide only: real BAC varies with food, medication, genetics and hydration, and no estimate makes it safe to drive.
Inputs
Result
0.056%
Estimate only — never use to decide whether to drive.
How the blood alcohol calculator works
Widmark: BAC % = (alcohol in grams ÷ (bodyweight in grams × distribution ratio)) × 100, with r about 0.68 for men and 0.55 for women.
One standard drink is roughly 14 g of pure alcohol — 350 ml of 5% beer, 150 ml of 12% wine, or 45 ml of 40% spirits.
Elimination is roughly linear at 0.015 percentage points per hour and cannot be accelerated. Subtract 0.015 × hours since the first drink.
Worked example: a 70 kg woman, three glasses of wine over two hours
- Alcohol consumed: 3 × 14 = 42 g.
- Body water mass: 70,000 g × 0.55 = 38,500 g.
- Peak BAC before elimination: 42 ÷ 38,500 × 100 = 0.109%.
- Less two hours of elimination: 0.109 − 0.030 = 0.079%.
- That is at or above the legal driving limit in most jurisdictions, and it will take over five more hours to reach zero.
Common mistakes to avoid
Assuming a pour is a standard drink
Home pours of wine are frequently double a standard measure, and craft beers often run 7–9% rather than 5%. Both silently double the estimate.
Believing coffee, food or a cold shower help
Nothing speeds elimination. Food slows absorption, lowering the peak, but the total time to sober is unchanged.
Treating an estimate as permission to drive
Widmark carries wide individual variance. Impairment begins well below legal limits, and the only safe plan after drinking is not driving.
Frequently asked questions
How long does alcohol take to leave the body?
Roughly one hour per standard drink, at about 0.015 BAC points per hour. A 0.08 BAC takes over five hours to clear.
Why do women reach a higher BAC than men?
Lower average body water proportion and less gastric alcohol dehydrogenase mean the same dose is distributed into a smaller volume.
Does eating lower my BAC?
Food slows gastric emptying and reduces the peak, but it does not reduce total alcohol absorbed or speed elimination.
Can I be over the limit the next morning?
Easily. Heavy evening drinking can leave measurable BAC eight to ten hours later, which is a common cause of morning-after offences.
How accurate is this estimate?
It is an approximation with substantial individual variance from genetics, medication, hydration and drinking pace. Never use it to judge fitness to drive.
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