Blood alcohol (estimate)

How it works

A «standard drink» contains about 10 g of alcohol (a glass of wine, a small beer, a shot). The Widmark formula estimates blood alcohol from weight and sex, minus elimination over time (~0.15 g/L per hour).

Warning

It's only a very rough ESTIMATE: the real value depends on many factors (food, metabolism, health). The legal driving limit in Italy is 0.5 g/L (0 for new drivers). When in doubt, do NOT drive: the only safe value is zero.

Why no calculation can tell you whether you can drive

The Widmark formula is a statistical estimate, not a measurement, and between two people of the same weight and sex the real value can differ by twenty or thirty per cent. It depends on lean mass (alcohol distributes into body water, not fat), on whether you've eaten, on how fast you drank, on medication, on the state of the liver, on age. No app and no sum know these things: the only reliable number is a breathalyser's, and the only safe value for driving is zero.

How long it really takes to clear

The body eliminates alcohol at an almost fixed rate, around 0.10-0.15 g/L an hour, and this is the part that surprises: it can't be sped up. Coffee, a cold shower, fresh air, moving about and eating afterwards don't remove a gram of alcohol from the blood — they wake you up, and that's the real danger, because they make someone feel clear-headed who isn't.

The practical consequence is arithmetic: someone reaching 0.8 g/L drops back under the 0.5 limit after about two or three hours, and back to zero after six or seven. It's why the morning-after check following a heavy night still finds people over: sleeping makes the time pass, not the alcohol.

The limits, and who has zero

In Italy the general driving limit is 0.5 g/L. But it's zero, with no tolerance at all, for anyone under 21, for anyone who has held a licence for less than three years and for professional drivers. Above 0.8 the penalties become criminal, and above 1.5 they reach arrest and confiscation of the vehicle. These are numbers worth knowing beforehand, not afterwards.

A practical detail almost nobody considers: in the first half hour to hour after drinking the level is still rising. Anyone getting behind the wheel «straight away, before it kicks in» is driving precisely while the value is climbing to its peak.

Nearby tools

If it's an evening with friends, the bill gets split with Group expenses and drink ideas are in Cocktail generator, which also explains how to make them without alcohol.