BAC Calculator
This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare provider for personal health decisions.
Widmark formula — estimated BAC only
How Blood Alcohol Concentration Is Estimated
Blood alcohol concentration (BAC) measures ethanol in your bloodstream as a percentage. The Widmark formula estimates BAC: BAC = (A × 5.14 / (W × r)) − 0.015 × H, where A is total alcohol consumed in ounces, W is body weight in pounds, r is the alcohol distribution ratio (0.73 for men, 0.66 for women), and H is hours since drinking started. Metric inputs convert to these units internally. A standard U.S. drink contains 14 grams (0.6 oz) of pure alcohol — one 12 oz beer at 5%, one 5 oz wine at 12%, or one 1.5 oz shot at 40%.
Example: a 180 lb (≈82 kg) man drinks 4 standard drinks over 2 hours. BAC = (4 × 5.14 / (180 × 0.73)) − 0.015 × 2 = (20.56 / 131.4) − 0.03 = 0.157 − 0.03 ≈ 0.127 (0.13%). The body metabolizes roughly 0.015% BAC per hour on average. Without the time factor, peak BAC would be about 0.16%. After 2 hours of metabolism, subtracting 0.03 yields the current estimate near 0.13%.
Impairment increases with BAC. Around 0.02–0.04%, mood elevation and slight relaxation appear. At 0.05–0.08%, judgment, coordination, and reaction time are measurably impaired — the U.S. legal driving limit is 0.08% in most states, with lower limits for commercial drivers and under-21 drivers. At 0.10%+, significant motor impairment occurs. Above 0.30% risks loss of consciousness and potentially fatal alcohol poisoning.
Individual variation is substantial. Food in the stomach slows absorption; carbonated mixers may speed it. Liver health, medications, tolerance, and genetics affect both peak BAC and metabolism rate. This calculator provides population-average estimates — a breathalyzer or blood test is the only reliable measure of actual BAC. Never drive based on a calculator result showing you are "under the limit."
Enter the number and type of drinks, your weight and sex, and elapsed time to estimate current BAC and time until sobriety (below 0.01%). Use it for educational awareness about alcohol's effects — the only safe BAC for driving is 0.00%.
Examples
| Example | Result |
|---|---|
| 180 lb male, 4 drinks over 2 hr | BAC ~0.13% |
| 140 lb female, 3 drinks over 1 hr | BAC ~0.14% |
| 200 lb male, 2 drinks over 1 hr | BAC ~0.04% |
| 130 lb female, 2 drinks over 2 hr | BAC ~0.06% |
| 170 lb male, 5 drinks over 3 hr | BAC ~0.12% |
| 150 lb female, 4 drinks over 3 hr | BAC ~0.11% |
| 220 lb male, 6 drinks over 4 hr | BAC ~0.10% |
| 120 lb female, 1 drink over 1 hr | BAC ~0.03% |
Frequently asked questions
In most U.S. states, 0.08% for adults 21+. Many countries use 0.05% or lower. Under-21 drivers and commercial drivers face stricter limits.
The body metabolizes roughly 0.015% BAC per hour on average — about one standard drink per hour. Coffee, cold showers, and exercise do not speed this up.
Women have a lower alcohol distribution ratio (less body water per kg) and often lower alcohol dehydrogenase activity, concentrating alcohol in the blood.