Blood Alcohol Content Calculator
Estimate your blood alcohol content from drinks, body weight, sex, and time using the Widmark equation.
A U.S. standard drink is 14 g of pure alcohol — roughly a 12 oz beer (5%), a 5 oz glass of wine (12%), or a 1.5 oz shot of spirits (40%). Your body clears alcohol at about 0.015% BAC per hour, which is why time matters as much as how much you drank.
This is a rough Widmark estimate, not medical or legal advice. Real BAC depends on food, medications, metabolism, and drink strength. Never use it to decide whether to drive.
How it works
This tool uses the Widmark equation, the same rough model police and researchers reference. It takes the grams of pure alcohol you drank, divides by your body weight times a distribution factor r (about 0.68 for men, 0.55 for women), and turns that into a BAC percentage.
Each standard drink counts as 14 grams of alcohol — roughly a 12 oz beer, a 5 oz glass of wine, or a 1.5 oz shot. Because your liver clears alcohol at about 0.015% per hour, we subtract that for every hour since your first drink, so the number falls the longer you wait.
Say you're a 70 kg man who's had 2 standard drinks over the last hour. The raw BAC works out near 0.059%, and after one hour of clearing you're around 0.044%. The calculator also estimates how long until you're back near zero.
Frequently asked questions
How accurate is this BAC estimate?
It's a reasonable ballpark, but no online tool can measure your real BAC. Food, medications, body composition, drinking speed, and how your liver works all shift the number. When in doubt, don't drive.
What counts as one standard drink?
In the U.S., a standard drink is 14 grams of pure alcohol: about a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot of 40% spirits. Cocktails and craft beers often count as more than one.
Can I use this to decide whether to drive?
No. This is an estimate, not a breathalyzer, and impairment can start well below 0.08%. If you've been drinking, the safe choice is to not drive at all.