Drink Drive Limit Calculator

In England, Wales, and Northern Ireland, the statutory blood alcohol limit is 80 mg of alcohol per 100 ml of blood (35 µg per 100 ml of breath) under the Road Traffic Act 1988. In Scotland, the limit was lowered under SSI 2014/328 to 50 mg of alcohol per 100 ml of blood (22 µg per 100 ml of breath).

There is no foolproof calculation for how many units correspond to statutory limits. Factors including body weight, biological sex, metabolism, and food consumption dramatically affect alcohol absorption. A single pint of strong craft ale or large glass of wine can place some drivers over the limit. Safety campaigns advise that the only reliable limit is zero drinks.

Our BAC calculator UK translates British beverage volumes (pints, metric glasses) and alcohol units (8 grams pure ethanol each) into estimated systemic blood concentrations (mg/100ml and breath µg/100ml). It then models hepatic zero-order elimination across realistic metabolic ranges (10 to 20 mg/100ml per hour) to show when alcohol is projected to clear.

Because the liver processes alcohol at an unrushable biological rate of approximately one unit per hour, multiple drinks consumed late at night can remain in your bloodstream well into the following morning or afternoon. Use our dedicated morning-after calculator to estimate your clearance timeline.