BAC Calculator
Estimate your blood alcohol content from your drinks, body weight and the time since you started drinking.
The Widmark formula
r is the share of body weight that alcohol spreads into: about 0.68 for men and 0.55 for women. The body removes roughly 0.015% per hour. Example: a 180 lb man who drinks three 12 oz beers (5%, about 42 g of alcohol) reaches a peak of about 0.076%; two hours after he started it is about 0.046%.
US limits
- 0.08% – legal limit for drivers 21 and over in every state except Utah.
- 0.05% – Utah.
- 0.04% – commercial drivers.
- Under 21 – zero tolerance, usually 0.02% or lower.
Impairment starts well below these limits: reaction time and judgment are affected from the first drink.
Why this is only an estimate
Food in the stomach, drinking speed, medicines, health and body composition all change real BAC. Never use a calculator to decide whether you can drive – the only safe level is zero.
Frequently asked questions
How many drinks put me over 0.08%?
It depends on weight, sex and time. A 180 lb man reaches about 0.08% after three to four standard drinks in an hour; a 140 lb woman after about two to three.
What is a standard drink in the US?
14 g of pure alcohol – a 12 oz beer at 5%, 5 oz of wine at 12% or 1.5 oz of 40% spirits.