What a BAC percentage means
BAC is commonly expressed as a percentage. For example, a BAC of 0.08% means 0.08 grams of alcohol per 100 millilitres of blood. Conventions and legal limits vary by jurisdiction, and can change; this site does not determine compliance with any legal threshold.
Why a calculator cannot measure your BAC
A calculator has to make assumptions about alcohol content, timing, body characteristics, absorption and metabolism. Food, health, medication, hydration, pace of drinking, and many other factors may affect a real person differently. Only an appropriate test can measure BAC.
Our methodology explains the Widmark-style assumptions used in the BAC estimate. The BAC estimate over time tool can illustrate how a model changes with time, but it cannot predict a safe moment to drive.
Impairment is not a simple threshold
Alcohol can affect judgment, reaction time, attention, coordination and decision-making before someone feels impaired. A person may be unsafe to drive or operate equipment regardless of a calculator output. Choose a sober driver, public transport, a taxi/rideshare, or another safe way home before drinking begins.
Use BAC information responsibly
Use the Blood Alcohol Calculator as an educational estimate of a reported scenario, not as permission to drive. You can also convert BAC formats or read what BAC is for a shorter introduction.