CalcVitalsBlood Alcohol Calculator — Widmark Estimate
The Widmark formula estimates blood alcohol from the alcohol consumed, your weight and sex. 56 grams of alcohol (four standard drinks) in a 70 kg man gives about 0.118% before any time passes — well over every driving limit — and it falls by only about 0.015% per hour. Nothing speeds that up.
How it works
The Widmark formula, from 1932, remains the standard back-calculation in forensic practice: alcohol distributes through body water, so the concentration is the dose divided by the water volume (a sex-specific fraction of body weight), minus a steady elimination rate of about 0.015% per hour. It is simple because alcohol's behaviour is comparatively simple — but individual variation around it is wide, which is why this page calls its output an estimate in every line.
Reference points for the grams field: a US standard drink contains 14 g of pure alcohol — that is a 355 ml beer at 5%, a 150 ml glass of wine at 12%, or a 44 ml shot at 40%. Real servings routinely exceed it: a pint of strong craft beer can hold 25–30 g, and a generous home pour of wine is often two standard drinks wearing one glass.
The safety message deserves its own paragraph. Driving limits (0.08% in the US and UK, 0.05% or lower across most of Europe, zero in many countries) are legal lines, not safe lines — impairment of reaction time and judgement begins with the first drink, and crash risk is measurably elevated at 0.05%. If this calculator is part of a decision about driving, the decision is already made: do not. Arrange the ride; the arithmetic will still be here tomorrow.
The method
Widmark: BAC% = alcohol(g) ÷ (r × weight kg) ÷ 10 − 0.015 × hours, where r = 0.68 (men) / 0.55 (women), the body-water distribution factors; elimination 0.015%/hour (population mean; true range ~0.010–0.025). Assumes drinking spread over the stated hours and completed absorption.
Frequently asked questions
How accurate is this estimate?
Within about ±0.02% for typical cases — good enough to show you are clearly over or clearly clear, never good enough to argue you are just under a limit. Food in the stomach lowers and delays the peak; fast drinking on an empty stomach does the opposite.
Can I sober up faster with coffee, food or exercise?
No. Elimination is done by liver enzymes working at a near-constant rate. Coffee gives you a more alert drunk person; food eaten before drinking slows absorption (lowering the peak somewhat) but does not speed clearance.
Why does sex change the result?
Two compounding reasons: women carry a lower fraction of body water for alcohol to dilute into (r = 0.55 vs 0.68), and on average have lower gastric alcohol metabolism. The same drinks in the same weight of body therefore produce a substantially higher BAC.