BAC Calculator — Blood Alcohol Estimate (Widmark)
Estimate your blood alcohol concentration from your drinks, body weight, sex and time since you started drinking, and see how it's likely to fall hour by hour. An educational estimate only — never use it to decide whether it's safe to drive.
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How Your Estimated BAC Falls
Hours after your first drink, assuming no more drinks and an elimination rate of 0.015% per hour (a commonly used, conservative figure).
| Hours After First Drink | Estimated BAC | vs 0.08% US Limit |
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How this calculator works
It uses the Widmark formula, the classic method for estimating blood alcohol:
- BAC (%) = alcohol (g) ÷ (body weight (g) × r) × 100 − 0.015 × hours
- r (the body-water distribution factor) = 0.68 for men and 0.55 for women, Widmark's average values
- Alcohol (g) = standard drinks × 14 g, or drinks × size (mL) × ABV × 0.789
- 0.015% per hour is a commonly used, conservative elimination rate; measured rates vary widely between people (roughly 0.009–0.035% per hour)
By Suhaib Hassan · Reviewed 28 September 2026 against NIAAA and NHTSA information · How CalculatePilot verifies formulas →
A worked example
A 176 lb (80 kg) man who has had 4 standard drinks (56 g of alcohol) over 2 hours: 56 ÷ (80,000 × 0.68) × 100 = 0.103%, minus 0.015 × 2 = about 0.073%. At 0.015% an hour, it would take roughly another 5 hours to fall to zero.
This is an estimate — not a safety determination
Real BAC depends on food, drinking speed, medications, health, body composition and individual metabolism, so your true BAC could be higher or lower than this estimate. Alcohol also keeps being absorbed for a while after your last drink, so BAC can still be rising. Impairment starts well below legal limits: NHTSA notes that even at 0.02% people show some loss of judgment and a decline in the ability to do two things at once. No calculator can tell you it's safe to drive. If you've been drinking, use a rideshare, taxi, public transport or a sober designated driver.
This page uses US figures. The legal limit for drivers 21 and over is 0.08% in every US state except Utah (0.05%); commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance laws. Limits differ in other countries, and being under a limit does not mean you are safe to drive.
Sources
- Widmark EMP. Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. Berlin: Urban & Schwarzenberg, 1932.
- Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Science International 2010;200:1–20.
- NIAAA — What is a standard drink?
- NHTSA — Drunk Driving
Frequently asked questions
How accurate is a BAC calculator?
It gives a rough, population-average estimate. Two people drinking the same amount can have very different BACs because of food, drinking speed, body composition, medications and metabolism. Only a breath or blood test measures BAC.
How long does it take for BAC to reach zero?
The body removes alcohol at a commonly estimated rate of about 0.015% per hour (a conservative figure; measured rates vary widely between people, roughly 0.009–0.035% per hour), and nothing — coffee, cold showers or exercise — speeds this up. A BAC of 0.08% takes about 5 hours or more to clear.
What counts as a standard drink?
In the US, a standard drink contains about 14 grams (0.6 fl oz) of pure alcohol — roughly a 12-oz beer at 5%, a 5-oz glass of wine at 12%, or a 1.5-oz shot of 40% spirits. Craft beers, large pours and cocktails often contain more.
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