An approximate blood alcohol figure by the Widmark formula. It is an estimate, never a licence to drive.
By the Widmark formula: divide the grams of pure alcohol by body weight times a distribution factor, roughly 0.68 for men and 0.55 for women. Then subtract for time, since the liver clears about 0.15 per mille an hour.
For an experienced driver the limit is 0.5 per mille; for a driver with under two years' experience and for professional drivers it is 0.2. This calculator gives an estimate, not a measurement, and no decision to drive should rest on an estimate.
The liver clears about 0.1–0.15 per mille an hour, and nothing speeds that up — not coffee, not a shower, not food. Going from 1.0 to zero takes seven to ten hours, so a morning drive after an evening of drinking can still be over the limit.
The Widmark formula is a statistical average, while the real level depends on food in the stomach, how fast you drank, metabolism, medication and body composition. Individual variation reaches thirty percent either way, so only a police measurement counts legally.