Answer: Enter your values and the BAC Calculator returns the exact result instantly — formula, worked example, and a plain-English explanation are included below the tool.
Estimate your Blood Alcohol Concentration
Blood Alcohol Concentration (BAC) is the weight of alcohol, in grams, per 100 milliliters of blood — expressed as a percentage. In 49 US states, a BAC of 0.08% or higher makes it illegal to drive a regular passenger vehicle — Utah is stricter at 0.05% — and commercial drivers are held to 0.04%. Drivers under 21 are subject to zero-tolerance laws, typically 0.01%–0.02%, in every state. Impairment of driving-relevant skills begins well below the legal limit — as low as 0.02% — which is why "below 0.08" does not mean safe. This calculator is an estimate only; actual BAC varies with metabolism, food intake, body composition, medication, and rate of drinking. Never drink and drive.
| BAC Level | Typical Effects | Legal Significance (US) |
|---|---|---|
| 0.02%–0.03% | Mild relaxation, slight mood change, some loss of judgment | Illegal under 21 in zero-tolerance states |
| 0.04%–0.05% | Lowered alertness, impaired judgment, reduced coordination | 0.04% limit for commercial (CDL) drivers |
| 0.06%–0.07% | Reduced muscle control, slower reaction, impaired reasoning | Approaching the per-se limit; some states impose penalties above 0.05% |
| 0.08%–0.09% | Poor balance, speech, and reaction time; impaired perception | 0.08% per-se limit in 49 states; Utah is 0.05% |
| 0.10%–0.12% | Marked impairment of motor control and judgment | Aggravating factor in sentencing in many states |
| 0.15%+ | Severe impairment; possible blackouts, vomiting, loss of consciousness | Enhanced-penalty threshold in most states (typically 0.15%–0.20%) |
This calculator uses the Widmark equation, the standard estimation method published by Swedish physician Erik Widmark in 1932 and still the basis of most BAC estimation today. The formula is: BAC = (A × 5.14 / (W × r)) − (0.015 × H), where A is the total ounces of pure alcohol consumed, W is body weight in pounds, r is the alcohol distribution ratio (0.73 for men, 0.66 for women, the widely used Watson/NIAAA-standard values), H is hours elapsed since drinking began, and 0.015 is the average metabolism (burn-off) rate — about one drink per hour for most people, per the National Institute on Alcohol Abuse and Alcoholism (NIAAA).
Each standard drink in the US contains 14 grams (0.6 fluid ounces) of pure alcohol: a 12-ounce beer at 5% ABV, a 5-ounce glass of wine at 12% ABV, or a 1.5-ounce shot of 80-proof (40%) spirits. Multiply the volume by the alcohol percentage to get the pure-alcohol content — for example, one 12-oz beer at 5% contains 0.6 oz of alcohol, exactly one standard drink. Heavier craft beers (7%+ ABV) and generous pours count as more than one drink each.
Worked example: a 180-lb man drinks 4 standard beers (2.4 oz pure alcohol) over 3 hours. BAC = (2.4 × 5.14 / (180 × 0.73)) − (0.015 × 3) = 0.094 − 0.045 = 0.049%, or roughly 0.05%. The same 4 beers would put a 140-lb woman (r = 0.66) at (2.4 × 5.14 / (140 × 0.66)) − 0.045 = 0.133 − 0.045 ≈ 0.088% — above the legal limit.
The Widmark formula is an average, and real bodies deviate from averages. Body fat matters: alcohol distributes in water, not fat, so at the same weight a person with higher body fat tends to reach a higher BAC — one reason the distribution ratio differs between sexes. Food slows absorption significantly; drinking on an empty stomach can nearly double peak BAC compared with drinking after a full meal. Rate of drinking matters because elimination runs continuously at roughly 0.015% per hour — spacing drinks out gives your body time to metabolize. Carbonated mixers speed absorption, medications (especially antihistamines and sedatives) interact with alcohol, and illness, fatigue, and altitude can amplify impairment. Breathalyzers and blood tests remain the only reliable measures of actual BAC.
Coffee, cold showers, exercise, and food do not lower BAC. Only time removes alcohol from the bloodstream — the liver metabolizes at a nearly fixed rate of about 0.015% per hour (one standard drink per hour), and nothing meaningfully speeds it up. Someone at 0.12% needs roughly 8 hours to reach 0.00%. A common and dangerous mistake is sleeping a few hours and driving in the morning while still legally drunk. Another myth is that beer is "safer" than spirits: BAC depends on total pure alcohol, so three beers and three shots of the same duration produce nearly identical blood-alcohol levels. Plan ahead: designate a driver, use a rideshare, or arrange to stay where you are.
How many drinks does it take to reach 0.08%? It depends on weight, sex, and time. As a rough guide using the Widmark formula, a 180-lb man reaches 0.08% after about 4 drinks in one hour; a 140-lb woman can exceed it after about 2–3 drinks in the same period. Spacing drinks over more hours lowers the estimate by 0.015% per hour.
What is the legal BAC limit in the US? 0.08% for drivers 21 and over in all 50 states. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance limits of 0.01%–0.02% depending on the state.
How long does alcohol stay in your system? The body eliminates alcohol at an average rate of 0.015% BAC per hour — roughly one standard drink per hour. At that rate, a BAC of 0.12% takes about 8 hours to return to zero. Urine and breath tests can detect recent use for somewhat longer.
Does drinking water or coffee lower BAC? No. Only time lowers BAC, because the liver metabolizes alcohol at a nearly constant rate. Water helps with dehydration but does not change your blood-alcohol level.
How accurate is a BAC calculator? BAC calculators use the Widmark formula, which estimates average behavior. Individual results vary with body composition, food intake, medications, and drinking pace — actual BAC can only be measured by a breathalyzer or blood test. Treat any estimate as approximate.