BAC Calculator
Estimate blood alcohol content from drinks, weight, and time — an estimate only
This is a rough estimate only. Many factors affect real BAC. Never use it to decide whether to drive — if you have been drinking, do not drive.
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Quick summary
Enter your number of standard drinks, body weight, sex, and hours since your first drink to estimate blood alcohol content using the Widmark formula. Your body eliminates roughly 0.015% BAC per hour. The US legal driving limit is 0.08%, but impairment begins well below that. This is a rough educational estimate — food, medications, health, and individual metabolism all affect real BAC, so never use it to decide whether to drive.
Reviewed by Simple Calculators TeamLast reviewed
For information only — not medical advice. Results are estimates from published formulas and can't account for your health history. Talk to a doctor or other qualified clinician before making health decisions.
How to use this calculator
- Enter the inputs requested by the calculator.
- Choose the units or options that match your situation and review the assumptions.
- Run or update the calculation to see the result.
- Review the result, breakdown, and formulas shown on the page.
- Check the inputs, units, dates, and limitations before saving or sharing the result.
Frequently asked questions
How is BAC calculated?
This calculator uses the Widmark formula: BAC ≈ (alcohol ÷ (body weight × a distribution ratio)) minus alcohol eliminated over time. More drinks and lower body weight raise BAC; time lowers it at about 0.015% per hour. It's an estimate — real BAC depends on many personal factors a formula can't capture.
What is a standard drink?
A US standard drink contains about 14 grams (0.6 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. Count each of these as one drink. Cocktails and craft beers often contain more than one standard drink.
How long does it take for BAC to reach zero?
Your body clears alcohol at roughly 0.015% BAC per hour, and that rate can't be sped up by coffee, food, or a cold shower. From a BAC of 0.08%, that's over 5 hours to reach zero. Only time lowers BAC. The calculator estimates the hours remaining.
Can I use this to decide if I can drive?
No. This is an educational estimate with a wide margin of error, and impairment begins below the legal limit. If you have consumed any alcohol, the safest choice is not to drive — use a rideshare, taxi, or designated driver. Never rely on a calculator to judge fitness to drive.
Key terms
- BAC
- Blood alcohol content, as a percentage of alcohol in the blood.
- Widmark Formula
- The standard equation for estimating BAC from drinks and weight.
- Standard Drink
- ~14 g of pure alcohol — one beer, glass of wine, or shot.
- Elimination Rate
- How fast the body clears alcohol — about 0.015% BAC per hour.
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.