A “measure” of alcohol depends on where you are and what you’re drinking. In the UK, a standard spirit measure is 25ml (about 1 unit of alcohol), while in the US, a standard drink is 1.5 fluid ounces of spirits, 5 ounces of wine, or 12 ounces of beer, each containing roughly 14 grams of pure alcohol. These aren’t interchangeable numbers, so knowing which system applies to you matters for tracking what you actually consume.
UK Spirit Measures
In UK pubs and bars, spirits like gin, rum, vodka, and whisky are served in legally defined measures: either 25ml or 35ml. A venue picks one size and sticks with it. They can serve multiples (a “double” is 50ml or 70ml), but they can’t mix both measure sizes on the same premises. This is set by law under weights and measures regulations.
A 25ml measure of a 40% ABV spirit contains exactly 1 UK unit of alcohol. A 35ml measure of the same spirit contains 1.4 units. If you order a double at a 25ml venue, that’s 2 units in your glass.
What Counts as One UK Unit
One UK unit equals 10ml (or 8 grams) of pure alcohol. That’s the baseline the NHS uses for tracking intake and setting health guidelines. To figure out how many units are in any drink, multiply the volume in milliliters by the ABV percentage, then divide by 1,000.
So a 175ml glass of 12% wine works out to: 12 × 175 ÷ 1,000 = 2.1 units. A 250ml large glass of the same wine jumps to 3 units. A pint (568ml) of 5% lager contains about 2.8 units. These numbers add up faster than most people expect, which is exactly why the formula is useful.
The US Standard Drink
The US doesn’t use “units.” Instead, the National Institute on Alcohol Abuse and Alcoholism defines one standard drink as any serving containing about 14 grams (0.6 fluid ounces) of pure alcohol. That’s roughly 75% more alcohol than a single UK unit.
In practical terms, one US standard drink equals:
- Beer: 12 ounces (a regular can) at 5% ABV
- Wine: 5 ounces at 12% ABV
- Spirits: 1.5 ounces (a standard shot) at 40% ABV
These are benchmarks, not rules about how drinks are actually poured. A craft beer at 8% ABV in a 16-ounce pint glass contains closer to two and a half standard drinks, not one. A generous restaurant wine pour of 6 ounces at 14% ABV is about 1.4 standard drinks.
Wine and Beer: Where Measures Get Tricky
Wine is where the gap between a “measure” and what you’re actually drinking tends to widen. In UK restaurants, wine comes in 125ml, 175ml, or 250ml glasses. A small 125ml glass of 12% wine is 1.5 units. A large 250ml glass of 14% wine is 3.5 units, nearly equivalent to a double spirit and a half.
Beer varies even more because ABV ranges so widely. A session lager at 4% in a pint gives you about 2.3 UK units. A strong craft IPA at 7% in the same glass delivers over 4 units. The glass size stays the same but the alcohol content nearly doubles, which the formula captures even if your intuition doesn’t.
Sweet wines and dessert wines are typically served in smaller portions of 2 to 3 ounces, but their higher sugar content often comes alongside higher ABV, so a small glass can still pack a full standard drink’s worth of alcohol.
How to Calculate Any Drink
Every bottle and can lists its ABV and volume. With those two numbers, you can work out the alcohol content of anything. The UK formula is straightforward: ABV × volume in ml ÷ 1,000 = units. For the US system, you can use the same logic but benchmark against 14 grams of pure alcohol instead of 10ml.
A few common examples:
- 330ml bottle of 5% beer: 1.65 UK units
- 750ml bottle of 13% wine: 9.75 UK units (roughly 7 US standard drinks)
- 25ml measure of 40% gin: 1 UK unit
- Pint of 5.2% craft lager: 2.95 UK units
The ABV is the number that matters most. Two beers in identical glasses can contain wildly different amounts of alcohol if one is a 3.5% table beer and the other is a 9% imperial stout.
How Much Is Considered Low Risk
The UK Chief Medical Officers recommend no more than 14 units per week on a regular basis for both men and women. That’s roughly six pints of average-strength beer or six 175ml glasses of 12% wine across an entire week. Spreading that over three or more days, rather than concentrating it into one or two sessions, further reduces health risks from long-term illness and from accidents.
In the US, dietary guidelines define moderate drinking as up to one standard drink per day for women and up to two for men. Because a US standard drink contains more alcohol than a UK unit, these two systems land in a similar range when you do the math over a full week.