Blood Alcohol Content (BAC) Calculator
Estimate your blood alcohol content from your weight, sex, number of drinks and time using the Widmark formula.
Updated October 2026
This is a rough Widmark-formula estimate, not a breathalyzer. Real BAC depends on food, medication, drinking pace, metabolism, hydration and more, and the elimination rate varies by person. Impairment begins well below 0.08%, and 0.05% or lower is the limit in many places. Never use this to decide whether to drive — if you've been drinking, don't.
This is an estimate for general information only and is not medical advice. Talk to a healthcare professional for decisions about your health.
TThe Crypto Tools69+ free crypto calculators — profit, fees, DCA and more.Our networkVisit →This calculator estimates your blood alcohol concentration (BAC) from your sex, body weight, how many standard drinks you've had and how long ago you started — using the Widmark formula, the method behind most online BAC estimates.
It's useful for understanding roughly how alcohol affects you and how long it takes to clear, but it is only an estimate. Your real BAC depends on many things this can't see, so treat the number as a ballpark, never as permission to drive.
How to use it
- 1Choose your sex and enter your body weight (the formula uses them to estimate how alcohol distributes through your body).
- 2Enter the number of standard drinks you've had — one standard drink is about 12 oz of beer, 5 oz of wine or 1.5 oz of spirits.
- 3Enter how many hours ago you had your first drink.
- 4Read your estimated BAC, whether it's over the 0.08% limit, and roughly how long until it clears.
Frequently asked questions
How is BAC calculated?+
This uses the Widmark formula: BAC = (grams of alcohol ÷ (body weight in grams × r)) × 100, minus about 0.015% per hour for elimination. 'r' is the distribution ratio — roughly 0.68 for men and 0.55 for women — reflecting that alcohol spreads through body water, which differs by sex.
What is one standard drink?+
In the US a standard drink contains about 14 grams of pure alcohol: roughly 12 oz of regular beer (5%), 5 oz of wine (12%), or 1.5 oz of 80-proof spirits (40%). Cocktails and craft beers often contain more than one standard drink, which is easy to underestimate.
How long does it take for BAC to reach zero?+
Your body eliminates alcohol at roughly 0.015% BAC per hour, and that rate can't be sped up by coffee, water or a cold shower. So a BAC of 0.08% takes about 5–6 hours to clear. The calculator shows an estimate for both reaching the legal limit and reaching zero.
Is a BAC under 0.08% safe to drive?+
No. 0.08% is the US legal limit for driving, not a safety threshold — meaningful impairment of reaction time and judgment begins well below it, and many countries set the limit at 0.05% or lower. The safest BAC for driving is 0.00%.
How accurate is this estimate?+
It's a rough approximation. Food in your stomach, medications, drinking speed, hydration, body composition and individual metabolism all change your actual BAC, and the elimination rate varies from person to person. Only a breathalyzer or blood test gives a real reading — never rely on this to decide whether to drive.
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