BAC Estimator
This BAC estimator uses the Widmark formula to estimate your blood alcohol content from the number of standard drinks, your body weight, and the time since your first drink — so you can see where you stand relative to the 0.08% legal limit.
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Your results
Estimate only — not legal or medical advice. Impairment begins well below 0.08%. Never drive after drinking.
How to use this calculator
Enter the number of standard drinks you have had, your body weight, your sex, and how many hours it has been since your first drink. Your estimated BAC updates as you type.
Example: a 180 lb man who has had 3 standard drinks over 1 hour has an estimated BAC of about 0.055% — below the 0.08% limit, but well into impaired territory. The math: (1.8 × 5.14) ÷ (180 × 0.73) − 0.015 = 0.0704 − 0.015 = 0.0554%.
How it works
The Widmark formula estimates blood alcohol content as:
BAC% = (A × 5.14) ÷ (W × r) − 0.015 × H
Where A is pure alcohol in fluid ounces (each standard drink = 0.6 fl oz), W is body weight in pounds, r is the distribution ratio (0.73 for men, 0.66 for women), and H is hours since the first drink — your body clears about 0.015% per hour. The result is floored at 0.00%. This is a rough estimate: food, metabolism, and medications all affect real BAC.
Frequently asked questions
What is BAC?
Blood alcohol content (BAC) is the percentage of alcohol in your bloodstream. A BAC of 0.08% - the legal driving limit in most US states - means 0.08 grams of alcohol per 100 mL of blood.
How accurate is this BAC estimate?
The Widmark formula gives a rough estimate only. Food, metabolism, medications, and drink strength all shift real BAC, so it can be off in either direction. Never use it to decide you are sober enough to drive.
How fast does BAC drop?
On average about 0.015% per hour - roughly one standard drink's worth. Coffee, cold air, and exercise do not speed it up; only time does.
Why does the calculator ask for sex?
The Widmark formula uses a distribution ratio (0.73 for men, 0.66 for women) that reflects average body water content, which affects how alcohol dilutes in the body.