What a unit of alcohol is
A unit is the UK's standard measure of pure alcohol: one unit is 10 millilitres (8 grams) of alcohol, roughly the amount an average adult body processes in an hour. Drinks vary so much in strength and size that "one drink" tells you very little, so units put a pint of beer, a glass of wine and a gin and tonic on the same scale.
The formula works because ABV (alcohol by volume) is simply the percentage of the liquid that is pure alcohol. Multiply the volume by ABV and divide by 100 and you get millilitres of pure alcohol; divide by 10 again to turn millilitres into units. Doing both steps at once means dividing by 1,000. A single 25 ml measure of 40% spirit is the neatest example: 40 × 25 ÷ 1,000 = 1, exactly one unit.
Units in common drinks
These figures use typical strengths, so check the label or pump clip for the drink in front of you. A stronger craft lager or a 14.5% red will carry noticeably more units than the standard versions below.
- Single spirit measure (25 ml, 40%): 1 unit
- Alcopop (275 ml, 4%): 1.1 units
- Half pint of beer (284 ml, 4%): 1.14 units
- Small bottle of lager (330 ml, 5%): 1.65 units
- Can of beer (440 ml, 4.5%): 1.98 units
- Double spirit measure (50 ml, 40%): 2 units
- Pint of beer (568 ml, 4%): 2.27 units
- Medium glass of wine (175 ml, 13%): about 2.3 units
- Pint of stronger lager (568 ml, 5.2%): about 2.95 units
- Large glass of wine (250 ml, 13%): 3.25 units
- Bottle of wine (750 ml, 13%): 9.75 units
The NHS 14 unit guideline
The UK Chief Medical Officers advise that both men and women are safest not drinking more than 14 units a week on a regular basis. The guidance also recommends spreading those units over three or more days rather than saving them for one or two sessions, and having several drink-free days each week. Fourteen units is about six pints of 4% beer (6 × 2.27 = 13.6 units) or six medium glasses of 13% wine (6 × 2.28 = 13.7 units).
Two points of context, stated as the guidance states them. First, 14 units describes a low risk level of drinking, not a safe one; no level of regular drinking has been identified as completely risk free, and the risks of illnesses such as cancer and liver disease rise with the amount drunk. Second, the guideline is the same for men and women, a change made in 2016 when the evidence was reviewed. The NHS advises women who are pregnant or trying to become pregnant not to drink at all.
Keeping track
The weekly tally in this tool multiplies one drink's units by how many of them you have in a typical week, which suits people whose drinking is fairly consistent. If your week mixes drinks, work out each one separately and add the results, or use a tracking app. The independent charity Drinkaware has a free one, along with unit information for thousands of specific drinks. Everything you enter here stays in your browser; nothing is uploaded or stored.
This tool is guidance, not medical advice. For information about alcohol and your health, or support with cutting down, see the NHS alcohol advice pages or speak to your GP.
Frequently asked questions
What is a unit of alcohol?
One unit is 10 millilitres (8 grams) of pure alcohol, the amount an average adult processes in roughly an hour. It is a UK measure designed to make different drinks comparable, because a pint of beer, a glass of wine and a shot of spirits all contain different amounts of alcohol.
How do I work out the units in a drink?
Multiply the ABV percentage by the volume in millilitres, then divide by 1,000. A pint of 4% beer is 4 times 568 divided by 1,000, which is 2.27 units. The formula works because ABV tells you what percentage of the liquid is pure alcohol, and one unit is 10 ml of it.
How many units are in a bottle of wine?
A 750 ml bottle at 13% ABV contains 9.75 units, so close to 10. At 12% it is exactly 9 units. A medium 175 ml glass of 13% wine is about 2.3 units and a large 250 ml glass is about 3.3 units.
What is the NHS guideline for alcohol?
The UK Chief Medical Officers advise that both men and women are safest not drinking more than 14 units a week on a regular basis, spread over three or more days, with several drink-free days. The guideline describes a low risk level, not a no risk level; no level of regular drinking has been identified as completely safe.
How long does alcohol stay in your system?
As a rough rule the body processes about one unit an hour, but only after alcohol has been absorbed, and the rate varies with body size, sex, food, liver health and other factors. This means it cannot be used to calculate when you are safe to drive; the only reliable approach is to leave plenty of time or not drive at all.