Blood Alcohol Content (BAC) Calculator
Blood alcohol content (BAC) is the concentration of alcohol in your bloodstream. The Widmark formula estimates it from the number of standard drinks, your body weight and sex, with a rough metabolism rate. It is an approximation only.
Enter the number of standard drinks, your weight and sex, and the hours since you started drinking. The calculator returns an estimated BAC. This is a rough guide and varies widely between individuals.
It gives a rough sense of how alcohol moves through the body over time — but it is a general estimate only, and must never be used to decide whether it is safe to drive.
Enter your values to see the result.
How this is calculated
This calculator estimates blood alcohol content (BAC) using the Widmark formula. It first converts the number of standard drinks to grams of alcohol (about 10 g per drink), then divides by body weight in kilograms times a distribution factor r — 0.68 for men, 0.55 for women — to give the theoretical BAC at the start of drinking. It then subtracts an average metabolism rate of about 0.015 per mille per hour for the hours since the first drink.
The distribution factor differs by sex because body water differs: the same alcohol amount produces a higher BAC in women than in men of the same weight. The metabolism term is an average; real clearance varies with liver function, genetics, food intake and medications.
The model is a rough approximation. It does not account for food in the stomach (which slows absorption), individual liver enzyme activity, medication interactions, age, fatigue, or the difference between a breathalyser and a blood test. Impairment begins well below legal limits, and individual variation is large. Never use any BAC calculator to decide whether it is safe to drive — if you drink, do not drive.
Worked example
A 75 kg man who has had 3 standard drinks over 2 hours.
- 1Alcohol grams = 3 × 10 = 30 g.
- 2BAC at time zero = 30 ÷ (75 × 0.68) ≈ 0.588 ‰.
- 3After 2 hours of metabolism = 0.588 − (2 × 0.015) ≈ 0.558 ‰ (about 0.056 g/dL).
Frequently asked questions
- What is a standard drink?
- It varies by country. Roughly 10–14 g of pure alcohol — a small beer, a small glass of wine, or a shot of spirits. Check your local definition and count carefully.
- Can I rely on this to decide whether to drive?
- No. Never use any BAC calculator to decide if it is safe to drive. Impairment begins well below legal limits, and individual variation is large. If you drink, do not drive.
- Why does sex matter?
- Body water differs by sex, so the same alcohol amount produces a higher BAC in women than men of the same weight. The formula uses different distribution factors accordingly.
- What is a standard drink?
- It varies by country, but roughly 10–14 g of pure alcohol — a small beer, a small glass of wine, or a shot of spirits. Check your local definition and count carefully, since a large poured drink can contain several standard drinks.
- Can I rely on this to decide whether to drive?
- No. Never use any BAC calculator to decide if it is safe to drive. Impairment begins well below legal limits, and individual variation is large. If you drink, do not drive.
Related calculators
Method: Widmark formula with sex-specific distribution factors and average metabolism. No external data source. Last updated: September 2026.
These results are general estimates from established formulas and are not medical advice. They depend on the accuracy of the values you enter and on individual factors the formulas cannot capture. Consult a qualified healthcare professional before making decisions about your diet, training or treatment.