What this calculator does
This blood alcohol calculator gives an educational estimate of blood alcohol concentration (BAC) using the Widmark equation, first published by the Swedish scientist Erik Widmark in 1932. You enter your weight, sex, how many US standard drinks you have had, and the hours since your first drink, and it returns an approximate percentage. It is a teaching tool for understanding how those inputs move the number, nothing more.
How the Widmark equation works
Widmark modelled BAC as the alcohol you have consumed spread through the water in your body, minus what your liver has already cleared. Each US standard drink is counted as 14 grams of alcohol. That total is divided by your body water, estimated as 0.68 of body weight for men and 0.55 for women, and then reduced by about 0.015 percent for each hour that has passed. The result is why a smaller person, or someone who drinks the same amount in less time, reaches a higher estimate.
Why the estimate is only an estimate
The equation assumes an average body and steady drinking, so it cannot capture the things that change real BAC. Food slows absorption. Medication, illness, hydration, and liver function all shift the result. Individual metabolism varies from person to person, and even the same person differs from day to day. Treat the number as a rough illustration, and never as a measurement you would act on.
Legal limits and staying safe
Legal driving limits are not universal. The US and many countries use 0.08 percent, others use 0.05 percent or lower, and some apply a zero limit to new or commercial drivers. This tool is not a legal reference, and it cannot tell you whether you are within any limit. The only reliable choice after drinking is to not drive at all and to arrange another way home.
Alcohol and your daily calories
Alcohol also carries energy that most food logs overlook, at about 7 calories per gram. A few drinks can add several hundred calories to a day without touching your meals. If you are tracking intake, the calorie calculator sets your daily target, and you can browse the full set on the calculators hub.
