Blood Alcohol Estimate (Widmark Equation)

This is an estimate and nothing more. It must never be used to decide whether someone can drive, work, or care for anyone. Erik Widmark's 1932 equation treats the body as a single well-mixed tank: alcohol spreads into the water-rich fraction of body mass, given by the distribution ratio $r$, and the liver removes it at a roughly steady rate thereafter. The first term is the peak the tank would reach, the second is what time has taken away.

Every part of that picture is an approximation. The distribution ratio varies with body composition, not just with sex, and the common values of 0.68 and 0.55 are population averages hiding a spread of roughly plus or minus 0.15. Elimination rates range from about 0.010 to 0.025 percent per hour between individuals and within one person on different days. Absorption is not instantaneous either: food in the stomach can delay and blunt the peak by an hour or more, so the equation can be badly wrong in the period right after drinking, which is exactly when people want to use it.

Forensic toxicologists still use Widmark, but they use it with measured blood samples, individualised parameters and stated uncertainty bands, and they report ranges rather than numbers. A result under any legal limit tells you nothing reliable about your actual blood alcohol, and impairment begins well below every legal limit in any case. If you have been drinking, do not drive.