Number One Blood Alcohol Calculator
Sketch the night. Not a reason to drive.
Set the clock for when drinking started and stopped, then drop beers, wine, spirits, or cocktails on the line. We estimate blood alcohol (BAC) through the night and show it against the limit for your region — in your browser, nothing uploaded.
A 12-hour clock. Pull the start and end around the face — it can run past midnight.
Duration
6 h
8:00 pm → 2:00 am
Drag a drink onto the line, or tap then tap the line.
This night stays in this tab. Refreshing clears it — nothing is stored.
Estimated blood alcohol
Do not drive on this number.
This night
Background
How this estimate is made
Glass sizes follow the region on the results badge — a US pint is not a UK pint — then we count them in UK units (one unit is 8 g of alcohol) so the sketch stays comparable. We use a Widmark-style estimate: grams of alcohol, divided by body weight and a sex factor (about 0.55 for women, 0.68 for men), with typical elimination of 0.015% per hour. Absorption is spread over about 40 minutes. That is a classroom model, not a lab result. Open “This night” under the chart for the drink count, units, and grams that went into it.
Error margins
Real blood alcohol often sits 20–40% away from a back-of-envelope curve. Food slows the peak. A larger or smaller body-water fraction changes the height. People eliminate alcohol somewhere around 0.010–0.020% per hour. Medications, illness, and the drink’s true strength all move the number. The band on the graph is that kind of slop. “Band under” on the cards is when the upper edge of that band falls below the limit — still not a legal reading.
Driving
Limits in law are measured from breath or blood, not from a website. The dashed line is the limit for the region on the badge. Change it if we guessed wrong: US and UK 80 mg/100 ml, much of the EU 50 mg, Japan 30 mg, Sweden 20 mg, some countries zero. Being under that line is not permission to drive. If you have drunk, do not drive. This calculator is for curiosity after the fact, not for planning a journey.