Blood Alcohol Content (BAC) Calculator
Estimate blood alcohol content from your drinks, weight and time. For education only — never use it to decide whether to drive.
Rideshare and designated-driver resources
Learn moreAn estimate, never a green light
This uses the Widmark formula to estimate BAC from alcohol consumed, body water and time. Real BAC varies with food, medications, health and individual metabolism, so the number can be off in either direction. Never use any calculator to decide whether to drive — if you’ve been drinking, don’t.
How it’s calculated & sources
BAC ≈ (drinks × 14 g) ÷ (body weight in g × r) × 100 − 0.015 × hours, where r is 0.68 (male) or 0.55 (female). Alcohol leaves the body at roughly 0.015% per hour.
Benchmark: 0.08% is the legal driving limit in most U.S. states (0.05% in Utah). This is an estimate for education only.
Results update as you type and are general estimates, not personalized financial, tax, medical or legal advice. Verify with a professional.
Worked example
Three standard drinks for a 170 lb male over 2 hours estimates around 0.05% — under the legal limit, but still impaired enough to affect driving.
Frequently asked questions
Can I rely on this to drive?
No. Individual variation is large and the stakes are deadly. If you have consumed alcohol, arrange a ride. The only safe BAC for driving is 0.00.
What raises my BAC fastest?
Drinking quickly, on an empty stomach, and at lower body weight. Food slows absorption but doesn’t prevent intoxication.