BAC Calculator
Adjust the inputs below. Results update as you type.
How it works
Uses the Widmark formula: BAC = (alcohol grams) / (weight kg × r × 10) − (0.015 × hours), where r is 0.55 for women and 0.68 for men. Estimates vary by metabolism, food intake, and medication. Legal driving limits are typically 0.08% in the US but lower in many countries. Never use this to decide whether to drive—the only safe amount before driving is zero.
Input guidance
- Use measured values (recent weight, height, activity level) rather than guesses.
- Recalculate every few weeks as your routine and body metrics change.
- Pair screening metrics with context such as sleep, stress, and medical history.
The formula
The Widmark formula: BAC = (alcohol grams ÷ (body weight g × r)) × 100 − (0.015 × hours), where r is about 0.68 for men and 0.55 for women.
Worked example
A 70 kg man having three standard drinks over two hours might reach roughly 0.05% BAC, though individual results vary widely.
More examples to test
- Maintenance case: keep activity constant and observe expected baseline ranges.
- Adjustment case: change only one major variable to understand sensitivity.
How to interpret results
Use results for awareness and planning, then validate with qualified medical or nutrition professionals for individualized decisions.
When this can be inaccurate
Population formulas cannot account for all biological factors such as medical conditions, medication effects, body composition differences, and genetics.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
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Frequently asked questions
How accurate is a BAC estimate?+
It is a rough approximation. Real BAC depends on food, metabolism, hydration, medications, and more, so never rely on it to decide whether to drive.
How fast does alcohol leave the body?+
Roughly 0.015% BAC per hour on average, but this varies by person. Time is the only thing that lowers BAC — coffee and water do not.
What BAC is over the limit?+
In most US states the legal driving limit is 0.08%, but impairment begins well below that. The safest choice is not to drive after drinking.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.