Blood Alcohol Content (BAC) Calculator

Blood Alcohol Concentration

BAC Calculator

Estimate your blood alcohol concentration based on what you drank, your body weight, and how long ago you started. For education, never as a green light to drive.

Step 1 of 3

A few things about you

Body composition affects how alcohol is distributed and metabolized. We use sex, weight, and time to apply the Widmark formula.

Sex assigned at birth Female Male

Body weight lbs Hours since first drink hr

Step 2 of 3

What did you drink?

Add the number of each drink you've had during the time window above.

Step 3 of 3

Your estimated BAC

Sober

.000

% BAC (estimate)

Estimated time to sober

0 hr

Time until below 0.08%

Already below

What you drank

This is an estimate, not a measurement. Real BAC depends on food, hydration, medications, body composition, and many other factors that the Widmark formula cannot account for. The only accurate way to measure BAC is a breathalyzer or blood test. Never use this calculator to decide whether to drive. If you've been drinking, do not drive. If you're worried about your drinking or someone else's, the SAMHSA National Helpline is free, confidential, and 24/7: 1-800-662-HELP (4357).

Fill out our confidential form whenever you're ready.

Your information stays private, and our team will respond with compassion, clarity, and the support you deserve.

How BAC works

The math, the metabolism, and the law

BAC isn't a vibe check. It's a measured number that climbs with every drink and falls at a fixed rate as your liver does its work.

BAC effect levels

A general guide. Effects vary person to person and rise sharply with combined drugs, fatigue, or empty stomach.

.00–.03 Subtle effects. Slight relaxation, minor mood changes. Reaction time and judgment are already lower than truly sober.

.03–.07 Mild to moderate impairment. Lowered inhibitions, reduced coordination, slower reaction time. Driving is risky even though you may feel fine.

.08–.15 Legally impaired. 0.08% is the per-se DUI limit in 49 states. Speech, balance, and self-control are all clearly affected.

.15–.25 Severe impairment. Major loss of balance and coordination, blurred vision, possible nausea. Risk of blackout climbs steeply.

.25+ Dangerous. Risk of unconsciousness, hypothermia, choking on vomit. Above about 0.30% can be fatal. Call 911 if you're worried.

The Widmark formula

Developed by Swedish physician Erik Widmark in the 1930s, the formula estimates BAC from grams of alcohol consumed, body weight, sex, and elapsed time. It's the foundation of most calculators, including this one.

Why sex matters in the math

Alcohol distributes through body water. Men's bodies are roughly 68% water by mass; women's are closer to 55%. Same drinks, same weight, but the woman's BAC will typically be higher. The formula uses these averages.

Metabolism is steady, not fast

The liver clears alcohol at roughly 0.015% BAC per hour, regardless of coffee, cold showers, or exercise. A BAC of 0.10% takes nearly seven hours to return to zero. Time is the only fix.

Why estimates miss

Food in your stomach slows absorption. Carbonation speeds it up. Medications, sleep, hydration, and individual liver enzymes all swing the real number. Treat any BAC estimate as a ballpark, not a permission slip.

U.S. BAC laws worth knowing

.08%49 states

Standard DUI per-se limit Driving with a BAC of 0.08% or higher is a criminal offense in every state except Utah. Lower BACs can still be charged if driving is impaired.

.05%Utah

Strictest in the nation Utah lowered its limit to 0.05% in 2018. It is the only U.S. state at this threshold (Utah Code §41-6a-502).

.04%CDL

Commercial drivers Anyone operating a commercial vehicle is subject to a stricter 0.04% federal limit (49 C.F.R. §382). On-duty commercial drivers are also barred from any alcohol within 4 hours of driving.

.02%under 21

Zero tolerance Every state enforces a near-zero BAC for drivers under 21, typically 0.00% to 0.02%. The legal drinking age is 21 nationwide under the National Minimum Drinking Age Act of 1984 (23 U.S.C. §158).

25%fatalities

The cost on the road Roughly 1 in 4 U.S. traffic fatalities involves an alcohol-impaired driver. NHTSA reports about 13,000 alcohol-impaired driving deaths in a typical year.

U.S. state-by-state BAC limits

All 51 jurisdictions

Adult limits are per-se driving thresholds. Under-21 limits are zero-tolerance values; some states define this as "any detectable amount." Penalties, license suspensions, ignition interlock rules, and look-back periods vary widely. Consult your state's official DMV or motor-vehicle code for current law.

SAMHSA National Helpline. 24/7, free, confidential. If alcohol is becoming a problem for you or someone close to you, this line offers information and treatment referrals in English & Spanish.

1-800-662-HELP

Sources

Widmark, E. M. P. (1932). Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. Foundational paper for the modern BAC formula.
National Highway Traffic Safety Administration, Drunk Driving. nhtsa.gov
Centers for Disease Control and Prevention, Impaired Driving: Get the Facts. cdc.gov
National Institute on Alcohol Abuse and Alcoholism, Understanding the Dangers of Alcohol Overdose. niaaa.nih.gov
National Minimum Drinking Age Act, 23 U.S.C. §158 (1984).
Federal Motor Carrier Safety Regulations, 49 C.F.R. Part 382 (commercial driver alcohol limits).
Utah Code §41-6a-502 (0.05% per-se limit).
SAMHSA National Helpline. samhsa.gov

BAC Calculator

A few things about you

What did you drink?

Your estimated BAC

What you drank

We can help you overcome addiction.

Fill out our confidential form whenever you're ready.

Support Is Available whenever you're ready!

A few things about you

What did you drink?

Your estimated BAC

What you drank

We can help you overcome addiction.

Fill out our confidential form whenever you're ready.

Support Is Available whenever you're ready!

You don't have to do this alone!

You don't have to do this alone!