How the blood alcohol (bac) calculator works
The Widmark formula, developed by Swedish chemist Erik Widmark in the 1930s, estimates blood alcohol from the grams of alcohol consumed, body weight and the share of the body that holds water.
r = 0.68 for men, 0.55 for women
A US standard drink contains 14 grams of pure alcohol: 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits. The body eliminates roughly 0.015% BAC per hour on average, though individual rates range from about 0.010 to 0.020. Food, medications, health and how fast you drink all change real results, so treat this as a rough guide.
Worked example
A 180 lb man has four standard drinks. The peak estimate is 56 g ÷ (81,647 g × 0.68) × 100 = 0.101%. Two hours after his first drink, about 0.03% has been eliminated, leaving roughly 0.071%. It would take nearly 5 more hours to return to zero. A 140 lb woman drinking the same amount over the same time would be at about 0.13%.
Frequently asked questions
What is the legal BAC limit for driving in the US?
0.08% in every state except Utah, where it is 0.05%. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance laws.
How long does it take to sober up?
On average BAC falls about 0.015% per hour, so a BAC of 0.08% takes over 5 hours to clear.
How accurate is a BAC calculator?
It is an estimate. Real BAC depends on food, drinking speed, body composition and metabolism. Only a breath or blood test measures it.
What counts as a standard drink?
14 g of alcohol: 12 oz of regular beer, 5 oz of wine, or 1.5 oz of 80-proof liquor.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.