BAC Calculator
Estimate Blood Alcohol Concentration (BAC) over time based on drinks consumed, body weight, and duration.
BAC Result
Medical disclaimer. This calculator is for general information and education only. It is not medical advice, not a diagnosis, and not a substitute for professional care. An estimated BAC is never a legal defence and must not be used to decide whether you are safe to drive. Absorption varies widely with food, medication, sex, body composition and how fast you drink; only an evidential breath or blood test is reliable.Speak to a doctor or another qualified clinician about any health decision.Last reviewed .
Frequently asked questions
What is BAC?
Blood Alcohol Concentration (BAC) measures the percentage of alcohol present in a person's bloodstream.
How does the Widmark formula estimate BAC?
BAC = (alcohol grams / (body weight in grams x r)) x 100, minus elimination over time, where r is the Widmark factor - roughly 0.68 for men and 0.55 for women, reflecting differences in body water. Alcohol is then cleared at about 0.015% per hour, which is close to constant regardless of how much you have drunk.
Why can this estimate be badly wrong for me?
Widmark assumes an average body composition and an average clearance rate. Food in the stomach, sex, age, liver health, medication, genetics and drinking pace all shift the result, and individual elimination rates vary by more than twofold. Treat any figure here as a rough illustration of how alcohol accumulates, never as evidence that you are under a limit.
Can I use this to decide whether to drive?
No. Never use a calculator to decide whether you are fit to drive. Legal limits differ by country and by licence class, impairment begins well below any legal threshold, and the only defensible reading is from a calibrated breathalyser or blood test. If you have been drinking, do not drive.