How is BAC calculated?

It uses the Widmark formula: grams of pure alcohol divided by (body weight in grams times a body-water constant), times 100, minus roughly 0.015% per hour for metabolism. The constant is about 0.68 for men and 0.55 for women.

How are grams of alcohol worked out?

From each drink: volume in ml × ABV/100 × 0.789 (the density of ethanol) × number of drinks. So a 330 ml drink at 5% ABV holds about 13 grams of pure alcohol.

Why does sex change the result?

The Widmark constant reflects the fraction of body weight that is water, which differs on average between men (~0.68) and women (~0.55). A lower constant means the same alcohol produces a higher BAC.

How does it estimate hours until sober?

It takes your peak BAC (before subtracting metabolism) and divides by the average elimination rate of 0.015% per hour, giving a rough time to reach zero.

What do the BAC bands mean?

As a rough guide: under 0.05% is below most legal limits, 0.05–0.08% exceeds many limits, and 0.08% and above is over the common driving limit and considered impaired. Limits vary by country and situation.

Can I use this to decide whether to drive?

No. The result is a rough estimate that ignores food, hydration, medication, genetics and many other factors. If you have been drinking, do not drive — the only safe BAC for driving is zero.

Is anything uploaded?

No. All calculations happen locally in your browser and nothing is sent anywhere.

Blood Alcohol Content (BAC) Calculator

Estimate blood alcohol content with the Widmark formula

This calculator estimates your blood alcohol content (BAC) from the number and strength of your drinks, your body weight and sex, and the time elapsed since your first drink. It is an educational tool for understanding how alcohol is processed, not a fitness-to-drive test.

How it works

First the tool finds the grams of pure alcohol you consumed:

grams = volume(ml) × ABV/100 × 0.789 × number of drinks

Then it applies the Widmark formula, where r is the body-water constant (0.68 for men, 0.55 for women):

BAC% = (grams ÷ (weight in grams × r)) × 100 − 0.015 × hours

The final term subtracts an average elimination rate of about 0.015% per hour. Hours until sober is the peak BAC divided by 0.015.

Example

A 75 kg man drinks 3 × 330 ml beers at 5% ABV, 2 hours ago:

grams = 330 × 0.05 × 0.789 × 3 ≈ 39.1 g
peak BAC = 39.1 ÷ (75,000 × 0.68) × 100 ≈ 0.0766%
after 2 hours: 0.0766 − 0.015 × 2 ≈ 0.0466% (below 0.05%)
hours to sober ≈ 0.0766 ÷ 0.015 ≈ 5.1 hours

Important: this is an estimate only. Real BAC varies widely between people and situations. Never use it to decide whether you are fit to drive — if you have been drinking, do not drive. Everything runs in your browser; nothing is uploaded.