How it works
The Widmark formula spreads the alcohol you drank (volume × ABV × 0.789 g/mL) through body water — 0.68 L/kg for men, 0.55 for women — and then subtracts an average elimination of 0.015 percentage points per hour.
BAC % = grams ÷ (kg × r × 1000) × 100 − 0.015 × hours
Tips
- Food, medication and fatigue change absorption — the real number can be much higher.
- Legal driving limits range from 0.00% to 0.08% depending on the country; zero is the only safe number.
- Everything runs in your browser; nothing is stored.
Standards and sources
- Searle J. (2015), Alcohol calculations and their uncertainty — Medicine, Science and the Law (PMC, NIH)
- Davies BT, Bowen CK (1999), Estimation of peak blood alcohol concentration in research and highway safety — AAAM (PMC, NIH)
- NIAAA (NIH) — What is a standard drink?
Last reviewed October 13, 2026
Frequently asked questions
Can I use this to decide whether to drive?
No. It is an average estimate and individuals vary by a factor of two or more. If you have been drinking, don’t drive.
What is a standard drink?
It depends on the country: 14 g of pure alcohol in the US, 10 g in Australia, 8 g (one unit) in the UK. Enter volume and ABV directly and the tool works out the grams.
Why is the result lower for heavier people?
The same amount of alcohol is diluted in more body water. Women usually have less body water per kg, so their factor is lower.