How to calculate alcohol in a drink
Written by The Kalcule Team · Last updated August 17, 2026
The blood alcohol calculator needs an alcohol dose. Dose comes from volume times alcohol by volume (ABV). This page shows that arithmetic so the inputs are not a guess.
Grams of ethanol
A common formula is volume (ml) × ABV × 0.789. A 330 ml beer at 5% is about 13 g of alcohol. Serving sizes on menus are not always what is poured.
Standard drinks differ by country
A “unit” in one country is not a “standard drink” in another. Type the actual volume and ABV into the calculator rather than counting vague “drinks.”
Home pours
Wine and spirits poured without a measure are the usual underestimate. Measure once so you know what your glass actually holds.
Then use the blood alcohol calculator
Dose, body weight, sex factor and time go into the Widmark estimate on the blood alcohol calculator. The result is still not a driving test.
Then type the grams into Widmark
Once you have volume and ABV, the blood alcohol calculator applies a simple Widmark estimate. Food, sex-specific body water and liver rate all scatter around that line. The page will never say you are fit to drive. Plan transport before the first drink.
Standard drinks versus what was poured
A UK unit, a US standard drink and an Australian standard drink are different masses of ethanol. Menu “glasses” of wine are often 175–250 ml, not a 125 ml tasting pour. Home spirits pours are usually larger than a 25 ml single.
Type millilitres and ABV. Counting two unnamed drinks is how people underestimate the dose. The arithmetic on this page exists so the blood alcohol calculator input is a real volume, not a guess.
What this arithmetic cannot tell you
Grams of ethanol are not impairment. Two people with the same dose can peak at different times. Mixing alcohol with medication is invisible to volume × ABV × 0.789. See what alcohol does and why you cannot sober up on demand.
If drinking is hard to control, stop doing drink math and get local help. Calculators are not treatment.
Frequently Asked Questions
Drink standard sizes and ABV.
US proof is twice ABV. A 80-proof spirit is 40% ABV.
They change volume and absorption speed, not the grams of ethanol unless they contain alcohol too.
Add the spirits by measured volume and ABV. Use a measured pour. Recipe text is often inexact.
Lower ABV and sometimes larger volumes. Calculate the grams, not the brand image.
Use millilitres. A UK pint is 568 ml. A US pint is 473 ml. Then multiply by ABV. Use the real container size, not the word beer.
Count the liquid you drank. A glass that was half foam is not a full pour of ethanol.
Estimate the fraction left and reduce the volume. Guessing that a leftover drink is zero makes logs and blood-alcohol estimates too low.
It is the approximate density of ethanol in g/ml used in the grams formula. The blood alcohol calculator can take drink entries without you calculating that yourself.
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