Blood Alcohol (BAC) Calculator
Estimate your blood alcohol concentration (BAC) from your weight, sex, the number of standard drinks and the time since your first drink, using the Widmark formula. This is a rough estimate only and must never be used to decide whether it is safe to drive.
How to use the BAC calculator
- Choose your weight unit, then enter your weight and sex.
- Enter how many standard drinks you have had and how many hours have passed.
- Read the estimated BAC and its status band, and remember it is only an estimate.
Examples
Two drinks, winding down
Male, 80 kg, 2 standard drinks, 2 hours
Estimated BAC 0.021 (Caution)
Three drinks, one hour
Female, 60 kg, 3 standard drinks, 1 hour
Estimated BAC 0.112 (Over US legal limit)
Frequently asked questions
What is blood alcohol concentration (BAC)?
BAC is the percentage of alcohol in your blood, written as grams of alcohol per 100 millilitres (for example 0.08 percent). In most US states a BAC of 0.08 percent or higher means you are legally too impaired to drive.
How does this calculator estimate BAC?
It uses the Widmark formula. Alcohol in grams (drinks times grams per drink) is divided by your body water in grams (weight in kilograms times 1000 times a distribution ratio of 0.68 for men or 0.55 for women), turned into a percentage, then reduced by about 0.015 per hour to model how your body removes alcohol.
What are the limitations of the Widmark formula?
It uses one average distribution ratio per sex and a single elimination rate, so it ignores body composition, food in your stomach, drinking pace, medications, health conditions and individual tolerance. Real BAC can be meaningfully higher or lower than the estimate.
Why is this only an estimate and not a real reading?
The only reliable way to know your BAC is a calibrated breathalyzer or a blood test. This tool cannot measure what is actually in your blood, so treat the number as a rough guide, not a measurement.
Can I use this to decide whether I am safe to drive?
No. Never use this estimate, or any online calculator, to decide whether to drive or operate machinery. If you have been drinking, do not drive. Impairment can begin below the legal limit, and the safest choice is always zero. When in doubt, call a taxi, use a rideshare or stay put.
Is my data sent anywhere?
No. The calculation runs entirely in your browser. Your weight, sex and drink count are never uploaded or stored.
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