Estimate blood alcohol content with the Widmark formula. Never drive after drinking.
Results are estimates for planning purposes and are not financial, medical, or professional advice.
How to Use the Blood Alcohol Calculator
BAC is the alcohol in your bloodstream as a percentage. This calculator estimates yours from your drinks, weight, and the hours since your first drink. A rough guide only, never a basis for driving.
- Count your drinks in standard drinks (guide below).
- Enter your weight and choose pounds or kilograms.
- Select male or female; body composition changes the result.
- Enter the hours since your first drink and press Calculate.
Blood Alcohol Calculator Formula
The Widmark formula: BAC% = (drinks × 0.6 × 5.14) ÷ (weight in lb × r) − 0.015 × hours. One standard drink holds 0.6 fluid ounces of alcohol; 5.14 converts it to blood concentration; weight is in pounds; r is 0.73 for men and 0.66 for women; 0.015 is the hourly elimination rate. Food, medication, and metabolism move the figure.
Example Calculation
A 180 pound man drinks four beers over two hours. Four drinks hold 2.4 ounces, so (2.4 × 5.14) ÷ (180 × 0.73) − 0.03 ≈ 0.064 percent, below the 0.08 limit. Impairment starts well below it, and one more drink takes him to about 0.087 percent. The same drinks give a 140 pound woman about 0.104 percent, over the limit.
What Counts as One Standard Drink
Enter standard drinks, not glasses. One holds 0.6 fluid ounces of pure alcohol, roughly what each of these servings contains:
| Drink | Serving | Strength | Standard drinks |
|---|---|---|---|
| Beer | 12 oz | 5% | 1 |
| Wine | 5 oz | 12% | 1 |
| Spirits | 1.5 oz shot | 40% | 1 |
Real servings run larger: a 16 oz craft pint at 7 percent is nearly two standard drinks, and an 8 oz wine pour 1.6.
How Long Until Your BAC Is Zero
Divide your BAC by 0.015, the hourly elimination rate. At 0.064 percent, about 4.3 more hours are needed; 0.08 takes over five hours to clear fully. Nothing but time lowers your BAC.
Frequently Asked Questions
What BAC is legally drunk?
In the United States and many other countries, 0.08 percent is the legal limit for drivers over 21. Commercial drivers face 0.04, and drivers under 21 face near-zero tolerance.
How accurate is a BAC calculator?
It is a reasonable estimate, not a measurement. Food, hydration, medication, and metabolism all shift the real number, so never use it to judge whether you can drive.
How long does alcohol stay in your system?
The body clears roughly 0.015 percent BAC per hour. A peak of 0.08 takes over five hours to fully clear, and only time, not coffee or cold air, speeds the process.
Why do women reach higher BAC than men from the same drinks?
Women typically carry less body water, so the same alcohol becomes more concentrated in the bloodstream. The Widmark formula reflects this with the lower 0.66 constant.
Can I drive if I feel fine?
Feeling sober is not a reliable test. Reaction time and judgment fade well below 0.08, so the only safe choice after drinking is not to drive.
What counts as one standard drink?
One standard drink is 0.6 fluid ounces of alcohol: a 12 oz beer at 5 percent, a 5 oz wine at 12 percent, or a 1.5 oz shot at 40 percent.
How long until my BAC returns to zero?
Divide the estimate by 0.015. A BAC of 0.06 needs about four more hours, and 0.08 needs over five. Only time lowers BAC.
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