Blood Alcohol (BAC) Calculator
Estimate blood alcohol content with the Widmark formula from drinks, body weight, sex and elapsed time.
🔒 Runs entirely in your browser — nothing is uploadedThe Widmark formula
The Widmark equation is the classic way to estimate blood alcohol content (BAC). In the form used here, BAC% = (A ÷ (W × r)) × 100 − β × H. A is the grams of pure alcohol consumed, W is body weight in grams, r is the Widmark distribution ratio (about 0.68 for men and 0.55 for women because of differences in body water), β is the elimination rate of roughly 0.015% per hour, and H is the number of hours since you began drinking. Each standard drink is counted as 14 grams of alcohol.
The first part of the equation estimates peak alcohol concentration based on how the alcohol spreads through body water. The second part subtracts what your liver has already metabolized over time. Because women on average have a lower proportion of body water, the same drinks produce a higher estimated BAC than for a man of equal weight.
What the numbers mean
BAC is expressed as a percentage of alcohol in the blood. In many places 0.08% is the legal driving limit for adults, but impairment of reaction time, judgment and coordination begins well below that — often from the very first drink. Lower limits apply to commercial and novice drivers in many regions, and some have near-zero limits. This calculator shades the status from "low" toward "high" as the estimate rises, purely as a rough visual guide.
Important safety and accuracy note
This estimate is a simplified average and can be badly wrong for any individual. Food in the stomach, hydration, body composition, metabolism, medications, drink strength, and how quickly you drank all change real BAC. Alcohol also continues to be absorbed for a while after your last drink, so a current estimate may understate your true peak. Never use this tool to decide whether it is safe to drive or operate machinery. If in doubt, do not drive. This page is for general information only and is not medical or legal advice. All calculations run locally in your browser and nothing is uploaded.
How to use
- Enter your detailsChoose units and sex, then enter your body weight.
- Add drinks and timeEnter the number of standard drinks and how many hours since you started.
- Read the estimateSee an estimated blood alcohol content with the Widmark formula and a caution note.