About blood alcohol content
This calculator gives a rough estimate of blood alcohol content (BAC) using the Widmark formula, from your sex, body weight, the number of standard drinks and the time since your first drink. It is for education and awareness only — actual BAC varies widely between people, and you should never use it to decide whether it is safe to drive.
How BAC works
How to use it
- Enter your sex and weight.
- Enter how many standard drinks you have had and over how many hours.
- Read the estimated BAC and impairment level.
The Widmark formula
BAC ≈ (alcohol in grams ÷ (body weight in grams × r)) × 100 − 0.015 × hours, where r is a body-water constant (about 0.68 for men, 0.55 for women). A standard drink is roughly 14 g of pure alcohol.
Important limits
This is only an estimate. Food, medication, health, drinking speed and individual differences all change real BAC. Never drink and drive — if you have had any alcohol, do not get behind the wheel.
Common uses
- Understand how drinks affect BAC
- See how time lowers BAC
- Compare drinks for awareness
- Learn about the Widmark formula
- Plan ahead for a night out
- Educate about alcohol limits
- Estimate impairment level
- Raise awareness about drink-driving
Frequently asked questions
How is BAC calculated?
With the Widmark formula, using your weight, sex, drinks and time since the first drink.
Is this accurate enough to drive?
No — it is a rough estimate and must never be used to decide whether to drive.
What is a standard drink?
About 14 g of pure alcohol — a 12 oz beer, 5 oz wine or 1.5 oz spirit.
Why does BAC fall over time?
The body removes alcohol at roughly 0.015% per hour, which the formula subtracts.
Why do men and women differ?
Body-water proportion differs, so the formula uses different constants.
Is my data uploaded?
No — it calculates entirely in your browser.
What affects real BAC?
Food, medication, health, drinking speed and individual metabolism.
Is it free?
Yes — completely free with no sign-up.