BAC Calculator

What is a BAC estimator?

A blood alcohol content (BAC) estimator estimates your blood alcohol level using the Widmark formula — from sex, weight, drinks consumed, and time elapsed. It’s an educational estimate, never a substitute for a breathalyzer or judgment.

How this calculator works

• Enter sex, body weight, number of standard drinks, and hours since the first drink.
• The Widmark formula distributes alcohol across body water using sex-specific ratios.
• It subtracts metabolism at roughly 0.015% BAC per hour.
• Hours-to-zero is estimated from the remaining BAC.

How to use the result

1. Never use this to decide if it’s safe to drive — estimates carry large individual error, and if in doubt, don’t drive.
2. Check the hours-to-zero figure to understand how long a night out lingers.
3. Count standard drinks honestly — craft beers, doubles, and large pours are more than one drink.
4. Compare to your local legal limit (0.08% in most US states; lower for commercial drivers and in some countries).

How accurate is a BAC calculator?

Within a range, but not precise. The Widmark formula is the standard forensic estimate, yet real BAC varies with food, body composition, medication, and drinking pace. Results can be 0.02% off either way — too wide a margin to rely on for a driving decision.

Common mistakes

• Using it as a driving decision tool. Estimates aren’t evidence; a breathalyzer is.
• Under-counting drinks. A “drink” is 12oz beer, 5oz wine, or 1.5oz spirits — most pours exceed this.
• Assuming coffee or showers speed metabolism. Nothing does — alcohol clears at a fixed rate.

BAC math is body-weight proportioning — the same logic behind the body fat calculator’s density formulas and the lean body mass calculator’s water-based estimates.