BAC calculator

The calculator uses the Widmark formula, the classic method for estimating blood alcohol:

BAC ≈ alcohol (g) ÷ (body weight (g) × r) − elimination × hours

• Alcohol in grams = volume × alcohol % × 0.789 (the density of ethanol).
• r (Widmark factor) reflects how much body water you have: about 0.68 for men and 0.55 for women. If you add your height, the calculator refines r from your BMI, because body composition matters.
• Elimination: the body removes roughly 0.010–0.015% BAC per hour. The calculator shows both ends as a band.

Each drink is assumed to be absorbed over about an hour, so the curve rises gradually instead of jumping.

In the U.S., one standard drink contains about 14 grams (0.6 fl oz) of pure alcohol:

Many craft beers, large pours and mixed drinks contain more than one standard drink. Use "Custom drink" to enter the exact size and percentage on the label.

A 180-lb man has two 12-oz beers at 5%, one hour apart. Each beer has about 14 g of alcohol, 28 g in total. With r = 0.68, the calculator estimates a peak around 0.02–0.03% and a return to roughly zero after about 3½ to 5 hours. A 140-lb woman drinking the same would peak at about 0.05–0.06%, because of her lower body weight and lower Widmark factor.

In every U.S. state it's illegal to drive with a BAC of 0.08% or higher; Utah's limit is 0.05%. Commercial drivers have a 0.04% limit, and drivers under 21 face zero-tolerance laws. But impairment starts well below the legal limit: reaction time, judgment and coordination are affected even at low levels.

Never use this calculator to decide whether you can drive. The estimate can be off in either direction, and a reading near zero doesn't mean alcohol has left your body. If you've been drinking, use a designated driver, a rideshare or public transit.

• Food in your stomach slows absorption and lowers the peak.
• Women generally reach higher BAC than men from the same amount.
• Medications, liver health, fatigue and individual metabolism change how fast alcohol is processed.
• Carbonated drinks and drinking quickly can raise the peak.

Only a breath or blood test measures actual BAC. If you're worried about your drinking, the NIAAA's resources or your doctor can help.

The result is shown as a percentage (grams of alcohol per 100 mL of blood), the unit used in the U.S. This is a rough educational estimate, not medical or legal advice. Your inputs are processed in your browser and never uploaded.