BAC Calculator

What BAC Measures

Blood Alcohol Concentration (BAC) represents the percentage of alcohol in your bloodstream by volume. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood — the legal limit for driving in all 50 US states. This calculator estimates your BAC based on your body weight, the number of drinks consumed, and the time elapsed since drinking.

The Widmark Formula

BAC estimation uses the Widmark formula: BAC = (alcohol consumed in grams / (body weight in grams × r)) − (0.015 × hours since first drink), where r is the Widmark ratio (approximately 0.68 for men and 0.55 for women). The 0.015 factor represents the average rate at which the body metabolizes alcohol per hour.

A standard drink contains roughly 14 grams of pure alcohol — equivalent to 12 oz of beer (5%), 5 oz of wine (12%), or 1.5 oz of spirits (40%). Two standard drinks for a 180-lb male over one hour yields approximately BAC = (28 / (81,647 × 0.68)) − (0.015 × 1) ≈ 0.035%.

Factors That Affect BAC

Body weight is the strongest factor — alcohol distributes through body water, so heavier individuals dilute alcohol more. Biological sex matters because of differences in body water percentage and the Widmark ratio. Food in the stomach slows absorption significantly — drinking on an empty stomach can produce a BAC 20-50% higher than the same amount consumed with a meal. Medications, fatigue, and individual metabolism also play roles.

Impairment Levels

At 0.02%, judgment begins to decline. At 0.05%, coordination and reaction time are noticeably affected. At 0.08% (the legal limit), muscle coordination, balance, and reasoning are substantially impaired. At 0.15%+, risk of vomiting, loss of balance, and blackout increases sharply. These thresholds are averages — some individuals show impairment at lower levels.

Important Limitations

This calculator provides an estimate only. Actual BAC depends on many individual factors that no formula can fully capture. The only way to measure true BAC is with a calibrated breathalyzer or blood test. Never use this calculator to decide whether you are safe to drive — if you have consumed any alcohol, use a designated driver, rideshare, or public transit.

Elimination Rate

The average person eliminates alcohol at about 0.015% BAC per hour (one standard drink roughly every 90 minutes), though this rate varies between 0.010% and 0.020%. Coffee, cold showers, and exercise do not speed up alcohol metabolism — only time reduces your BAC.

Authoritative Sources

This calculator uses formulas and reference data drawn from the following sources:

- CDC — Physical Activity - NIH — National Institute of Diabetes - NIH — National Heart, Lung, and Blood Institute

This bac calculator uses standard health formulas to compute results. Enter your values and the formula is applied automatically — all math is handled for you. The calculation follows industry-standard methodology.

• https://www.nih.gov
• https://www.who.int
• https://www.cdc.gov