Read this first: never drive after drinking
No calculator can tell you whether you are safe or legal to drive. This page produces a rough mathematical estimate from averages, and real blood alcohol varies widely between people and occasions. The only safe choice is never to drive after drinking — plan a sober driver, a taxi or a ride-share before the first drink, not an estimate after the last one. Legal limits vary by place: 0.08% is the common US limit for adult drivers, but lower limits apply to commercial drivers and to drivers under 21 in the US, many countries set 0.05% or lower, and some enforce effectively zero. Being under a legal limit is not the same as being unimpaired — judgement and reaction time deteriorate from the first drink. Know the signs of alcohol poisoning: confusion, vomiting while semi-conscious or unconscious, seizures, slow, irregular or stopped breathing, and pale or bluish skin. If someone shows them, call emergency services immediately and stay with them — that is a medical emergency, not something to sleep off.
The Widmark formula
Swedish chemist Erik Widmark's model, still the standard first approximation, treats alcohol as distributing through the body's water. The factor r estimates the share of body mass that is water available for that distribution: about 0.68 for men and 0.55 for women on average, which is why the same drinks produce a higher BAC in a smaller or female body. The formula first computes a peak — the BAC if all the alcohol were absorbed instantly — then subtracts elimination at an average of 0.015% per hour for the time since drinking started. Both averages hide wide individual variation, which is why every figure on this page is an estimate only.
What counts as one standard drink?
In the United States, one standard drink contains about 14 grams of pure alcohol. That is a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot of spirits at 40%. Real drinks routinely break the standard: craft beers run 7–9%, wine pours at home are generous, cocktails often hold two or three shots, and a large glass of strong wine can equal two standard drinks by itself. If your drinks were stronger or larger than standard, raise the alcohol-per-drink field above 14 g or count the drinks honestly upward — underestimating the input guarantees an underestimated result, in the dangerous direction.
Elimination, and the myths that do not speed it up
The body clears alcohol at a roughly constant rate — about 0.015% per hour on average, with real rates ranging roughly from 0.010% to 0.025% — and essentially nothing speeds it up. Coffee does not; it makes a drowsy drinker feel more awake while remaining exactly as impaired, which is arguably worse. Food after drinking does not; food before and during drinking can slow absorption and lower the peak somewhat, but it does not remove alcohol already in the blood. Fresh air, cold showers, exercise and vomiting after absorption do not meaningfully change BAC. Only time lowers it, which is why this calculator reports hours to zero — and why "I feel fine now" a couple of hours after heavy drinking can still mean a BAC well above the legal limit.
Worked example
An 80 kg man drinks 4 standard drinks (4 × 14 g = 56 g of alcohol) starting 1 hour ago. Peak = 56 ÷ (80,000 g × 0.68) × 100 = 0.103%. Elimination removes 0.015% × 1 hour, so the estimated BAC now is 0.103 − 0.015 = 0.088% — above the common 0.08% US limit — and reaching zero takes about 0.088 ÷ 0.015 ≈ 5.9 more hours. Estimate only: never drive on the strength of it.
How to use this calculator
- Select male or female so the calculator uses the matching Widmark body-water factor.
- Enter your body weight and choose kilograms or pounds.
- Count your standard drinks honestly — strong or oversized drinks count as more than one — and check the grams per drink.
- Enter the hours since drinking started, then read the estimated BAC now and the hours to zero.
- Whatever the estimate says, do not drive after drinking: arrange a sober ride instead.
Why your real BAC could be higher — or lower
Widmark's averages smooth over almost everything that makes real bodies differ. Food in the stomach slows absorption, so the same drinks on an empty stomach peak higher and sooner. Medications, fatigue, illness and hormonal factors can change both absorption and how strongly a given BAC impairs you. Body composition matters beyond the two r values: alcohol does not distribute into fat, so two people of equal weight but different body fat genuinely reach different levels — neither r value knows which one you are. Pouring and strength errors compound all of it, almost always in the direction of more alcohol than counted. And tolerance changes how drunk someone feels without changing their BAC at all — feeling steady is not evidence of a low level.
Breathalysers and blood tests measure; this page only estimates, and its error bars easily span the difference between legal and illegal. Law enforcement in most places can also charge impairment below the headline limit. So use the number here for understanding — how drinks, weight and time interact, and how long alcohol genuinely stays in the system — and never as permission. If you drank, do not drive. If someone near you shows signs of alcohol poisoning, call emergency services first and ask questions later. Estimates only, not medical or legal advice.
Important note
For information only — not medical advice. This calculator uses standard published formulas to estimate values for general education and planning. It does not diagnose, treat, or replace the advice of a doctor or other qualified health professional. If you have a health concern, are pregnant, or are making decisions about treatment, medication, or a major diet or exercise change, please talk to a healthcare professional first.