Blood Alcohol Calculator
This blood alcohol calculator uses the Widmark formula, a population-average estimate, to approximate blood alcohol concentration (BAC) from body weight, sex, number of standard drinks, and hours since drinking began. It is an educational estimate only: individual factors like food intake, medication, metabolism, and drink strength cause real BAC to vary significantly from this formula. This tool must never be used to decide whether it is safe or legal to drive — only a breathalyzer or blood test gives an actual reading.
Educational estimate only. Results are not medical, legal, or financial advice. Confirm important decisions with a qualified professional.
How it works
- Choose your sex and enter body weight.
- Enter standard drinks consumed and hours since the first drink.
- Read the estimated BAC — an educational figure only, not a legal or safety determination.
Formula BAC% = (drinks×14g / (weightKg × r × 1000)) × 100 − 0.015×hoursElapsed, r = 0.68 (men) or 0.55 (women)
Frequently asked questions
Is this calculator accurate enough to decide if I can drive?
No. This is an educational estimate only. Real BAC depends on factors this formula cannot capture, such as food, medication, and individual metabolism. Never use it to judge fitness to drive — use a breathalyzer or simply do not drive after drinking.
What is the Widmark formula?
It is a population-average formula from 1932 that estimates BAC from alcohol consumed, body weight, sex-based distribution ratio, and elimination over time.
What counts as a standard drink?
This tool uses the US standard of 14 grams of pure alcohol, roughly one 12 oz beer, one 5 oz glass of wine, or one 1.5 oz shot of spirits.
Why does sex change the result?
The Widmark formula uses a different alcohol distribution ratio for men and women, reflecting average differences in body water content.
Why does the estimate go down over time?
The formula subtracts a standard elimination rate of about 0.015% BAC per hour to reflect the body metabolizing alcohol over time.