How this instrument works
The UK's alcohol unit is a fixed quantity, not a serving size: one unit equals 10 ml, or 8 grams, of pure alcohol, regardless of what the drink is or how large the glass. To convert any drink into units, multiply its volume in millilitres by its strength — alcohol by volume, as a percentage — then divide by 1000. The formula is defined by the NHS, on the same page it uses to explain the country's drinking guidelines.
The system exists because a 'drink' on its own is a wildly inconsistent measure — a small strong spirit and a large weak beer can contain a similar amount of actual alcohol, or very different amounts, depending on volume and strength. Converting everything to a common 10 ml measure lets someone add a pint, a glass of wine, and a spirit mixer from one evening into a single meaningful total, rather than a headcount of glasses that means little on its own.
Units measure alcohol content only; they say nothing about food eaten alongside a drink, body weight, sex, medication interactions, or tolerance built up over years of regular drinking, all of which change how a given number of units actually affects someone. The UK's Chief Medical Officers set the current guidance — no more than 14 units a week on a regular basis, spread across three or more days with some drink-free days included — as a population-level low-risk threshold, not a personal target. Drinking right up to that line every week still carries measurable long-term health risk; it is simply the point past which the evidence gets clearer.
- Enter Drink volume (volume) in millilitres, litres, or fluid ounces — a bottle label usually states this directly.
- Enter the drink's ABV (abv) as a percentage; check the bottle or can, since it varies even within one drink type.
- Read UK alcohol units (units) — the calculator multiplies volume by ABV and divides by 1000 for you.
- Repeat for each drink across a session or week and add the results to compare against the 14-units-a-week guidance.
Worked example — a pint, a wine glass, a spirit measure
A UK pint of beer is 568 ml. At 4.5% ABV, the sum is 568 × 4.5 ÷ 1000 = 2.556, which rounds to about 2.56 units — over a quarter of the entire weekly 14-unit guidance in a single pint.
A standard 175 ml glass of wine at 12% ABV: 175 × 12 ÷ 1000 = 2.1 units exactly — two such glasses already account for nearly a third of the weekly guidance.
A single 25 ml spirit measure at 40% ABV: 25 × 40 ÷ 1000 = 1.0 unit exactly. That is not a coincidence — it is the reference pour the entire units system was calibrated to make intuitive, one unit per standard measure.
Questions
How many units are in a pint of beer?
A standard UK pint (568 ml) of 4.5% beer works out to about 2.56 units, using volume in millilitres times ABV percentage divided by 1000. Stronger beers push the figure higher and weaker session beers push it lower, so the ABV printed on the can or pump clip matters as much as the pint measure itself.
What counts as a unit of alcohol in the UK?
Exactly 10 ml, or 8 grams, of pure ethanol — a fixed physical quantity defined by the NHS and used across UK drinking guidance, independent of drink type, glass size, or price. A small strong drink and a large weak one can contain the same number of units.
How many units a week does UK guidance recommend?
No more than 14 units a week on a regular basis, for both men and women, spread across three or more days rather than concentrated into one or two heavy sessions, with some drink-free days included. This is the UK Chief Medical Officers' current low-risk guidance, not a target to drink up to.
Is a UK unit the same as a US standard drink?
No. A US standard drink is defined as roughly 14 grams of pure alcohol, while a UK unit is 8 grams — so one US standard drink equals about 1.75 UK units. Comparing weekly totals across the two countries without converting between the two systems will misjudge how much a given figure actually represents.
Does ABV alone tell me how many units are in a drink?
No — volume matters just as much. A small glass of a strong drink and a large glass of a weak one can land on the same unit count, or very different ones; both volume and ABV percentage have to go into the formula together. Reading ABV off a label without accounting for how much you are actually pouring will misjudge the total.
Why does the units formula divide by 1000?
Because two conversions happen at once: dividing by 100 turns the ABV percentage into a plain fraction, giving the millilitres of pure alcohol in the drink, and dividing that by a further 10 converts millilitres of pure alcohol into units, since one unit is defined as 10 ml. Multiply those two divisors together, 100 by 10, and you get the single constant, 1000, the formula divides by in one step.
References
- NHS — Alcohol units (calculating alcohol units)
- UK Chief Medical Officers' Low Risk Drinking Guidelines (2016)
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.