BAC Calculator: Estimate Your Blood Alcohol Content

Blood alcohol content (BAC) is the number police officers, courts and breathalyzer machines use to decide whether a driver is legally impaired. Our free BAC calculator estimates your blood alcohol level from what you drank, your body weight, your sex and how much time has passed — using the same Widmark formula that researchers and courts have used for decades.

Important: This calculator gives an estimate only. Your real BAC depends on food, body composition, medication, health and other factors no calculator can measure, and a police breathalyzer or blood test can read higher or lower than any estimate. A result below the legal limit does NOT mean you are under the limit or safe to drive. The only safe BAC for driving is 0.00%. Never drive after drinking.

What Counts as One Standard Drink?

In the United States, one standard drink contains about 0.6 ounces (14 grams) of pure alcohol. That equals:

• Beer: 12 oz at 5% alcohol (a regular can or bottle)
• Wine: 5 oz at 12% alcohol (a typical glass)
• Spirits: 1.5 oz at 40% alcohol / 80 proof (one shot of whiskey, vodka, tequila or gin)
• Malt liquor: 8–9 oz at 7% alcohol

Craft beers, large pours and mixed drinks often contain 1.5 to 2 standard drinks each. When in doubt, count them as more, not less — a strong drink raises your BAC more than this calculator’s standard servings.

How This BAC Calculator Works

The calculator uses the Widmark formula, the standard scientific method for estimating BAC: Estimated BAC = (ounces of pure alcohol × 5.14) ÷ (body weight in pounds × r) − (0.015 × hours since the first drink). The factor “r” is 0.73 for men and 0.66 for women, because alcohol spreads through body water and men carry a higher share of water on average. The 0.015 figure is the average rate at which the body eliminates alcohol every hour. Nothing speeds this up — not coffee, food, cold air or exercise. Only time brings BAC down.

BAC Levels and Their Effects

• 0.02% — Slight relaxation and mood change; judgment already beginning to shift.
• 0.05% — Lowered alertness and coordination; crash risk roughly doubles. This is the legal limit in Utah.
• 0.08% — The legal limit in all other states. Muscle coordination, reaction time and judgment are clearly impaired.
• 0.15% — Major loss of balance and control; vomiting and blackouts become possible.
• 0.20% — Confusion, slurred speech, possible loss of consciousness.
• 0.30% and above — Life-threatening: alcohol poisoning, coma and death are real risks. Call emergency services.

Legal BAC Limits in the United States

• 0.08% — the per se limit for drivers 21 and over in 49 states.
• 0.05% — Utah’s limit, the strictest in the country.
• 0.04% — the limit for commercial (CDL) drivers.
• 0.00–0.02% — zero-tolerance limits for drivers under 21 in every state.

Driving at or over these limits is a DUI (or DWI) offense even if you feel fine, and penalties escalate fast: fines, license suspension, ignition interlock and jail time. Remember that an officer can also arrest you below the limit if your driving shows impairment. If you have been stopped after drinking, it helps to understand your rights around breath tests — read our guides on whether you can refuse a police breathalyzer test and whether you can refuse a field sobriety test.

How Long Does Alcohol Stay in Your System?

Your body removes alcohol at roughly 0.015% BAC per hour, so a BAC of 0.08% typically takes about 5 to 6 hours to reach zero. Alcohol can be detected for much longer than the impairment lasts: roughly up to 24 hours on a breath test, 12 to 72 hours in urine (longer with EtG tests), up to 90 days in hair, and about 12 hours in blood. “Sleeping it off” only works because time passes — you can wake up still over the limit after a heavy night.

Factors That Affect Your BAC

• Body weight and composition — alcohol concentrates in body water, so the same drinks produce a higher BAC in a smaller person.
• Sex — women generally reach a higher BAC than men of the same weight after the same drinks.
• Food — drinking on an empty stomach speeds absorption; food slows it but does not reduce the final peak by much.
• Speed of drinking — drinks consumed quickly stack up before the body can eliminate alcohol.
• Drink strength — craft beers, doubles and generous pours contain more alcohol than standard servings.
• Medication and health — some medications and conditions intensify alcohol’s effects.

Use this calculator to understand how alcohol adds up — not to test how close to the limit you can get. If there is any doubt at all, choose a sober driver, a taxi or a rideshare. A DUI costs thousands of dollars and can cost far more than money.