The Formula's Anatomy
Erik Widmark's 1932 equation assumes alcohol distributes through total body water, which is what r approximates, men average ~68% water, women ~55%. A standard drink (14 g of pure alcohol) raises the BAC of a 75 kg man by roughly 0.02%.
Time enters as a linear subtraction: 0.015% per hour, the population-average elimination rate.
Why Estimates Wander
Absorption is the wildcard. Food in the stomach slows it dramatically, so the same drinks can peak 30% lower, or higher, if the drinks arrived fast on an empty stomach.
Elimination varies with liver health, genetics, and chronic drinking patterns. Body composition also matters: r assumes average body fat, but fat holds far less water, so two people of equal weight can dilute alcohol differently.
What a Calculator Is — and Is Not
The Widmark estimate is a useful educational window into a session's trajectory, typically within ±0.02% for average adults.
It's never a permission slip. Breathalyzer-grade certainty belongs to calibrated devices, and driving decisions belong to the rule: if you drank, don't.
Sources
FAQ
How accurate is the Widmark formula?
Within roughly ±0.02% for average adults under typical conditions, but food, medications, and individual metabolism can push it further.
Why is the r factor lower for women?
Women average less body water per kilogram, so the same alcohol dose concentrates in a smaller water volume, a higher BAC.
Does food really change BAC?
Yes, food slows stomach emptying and absorption, lowering the peak by a meaningful margin versus drinking on an empty stomach.
A note before you begin: this tool offers educational estimates only. It cannot replace advice from a qualified professional.