Alcohol leaves the blood at roughly 0.015 g/100 mL an hour and nothing speeds that up — but no calculation of it tells you when you are fit to drive. The only reliable rule is not to drink and drive at all.
Elimination is close to constant per hour, so a rough clearance time can be arithmetic. What cannot be computed is the thing people actually want: whether THIS person is impaired now. Individual elimination varies by a factor of two and a half across healthy adults, the distribution of alcohol through the body varies with composition no formula measures, and impairment of reaction time and judgement is present well below every legal limit in the world. A limit is where a legislature decided to prosecute, not where risk begins.
Everywhere. It fails hardest the morning after, when people have slept and feel recovered while alcohol is still being cleared, and it fails for anyone estimating from remembered drinks — home measures are not measures, and the memory is usually a bigger error than the model. Treat any computed figure, including the one on this site, as an illustration of a formula rather than a fact about a person.
Estimate with the rule, then check it against the calculator that models it properly.
Open Blood Alcohol Curve →Alcohol leaves the blood at roughly 0.015 g/100 mL an hour and nothing speeds that up — but no calculation of it tells you when you are fit to drive. The only reliable rule is not to drink and drive at all. Elimination is close to constant per hour, so a rough clearance time can be arithmetic.