UK Alcohol Units Explained: How They Are Calculated and Used

What is a UK alcohol unit?

A UK alcohol unit is a fixed amount of pure ethanol — 10 millilitres, or 8 grams — chosen by the Department of Health in 1987 as a round number that roughly matches what an average adult liver clears in an hour. Every drink you buy in the United Kingdom, regardless of brand or style, can be expressed as a number of these units once you know its volume and its alcohol-by-volume percentage. The alcohol units calculator does that arithmetic for any drink: enter the size of the pour in millilitres, the ABV from the label, and the number of drinks, and it returns the unit total along with the share of the UK weekly low-risk limit it represents.

The unit is not a marketing convenience. It is the basic currency of every piece of UK guidance on drinking — the NHS, the Department of Health and Social Care, Drinkaware, the Chief Medical Officers’ 2016 Low Risk Drinking Guideline, and the alcohol labels mandated by the Portman Group’s Code all measure consumption in units rather than drinks. Whenever a doctor asks how many units a week you drink, or a public-health campaign quotes a 14-unit ceiling, this is the number they mean. Counting in units rather than drinks lets a half-pint of weak ale and a single shot of strong spirits be compared on the same scale, which is the whole point of the system.

It also explains why the unit is uniquely British. An Australian standard drink is 10 grams of ethanol; an American standard drink is 14 grams; Dutch and Austrian standards match the UK at 8 grams, while Italy goes up to 12 grams and Japan all the way to 19.75 grams. Translating between systems is straightforward arithmetic but it is rarely done in the wild, so guidance written for one country generally cannot be applied directly to another. The numbers on this page, and in the alcohol units calculator, are UK units throughout.

How alcohol units are calculated

The NHS formula is one line:

units = ABV% × volume (ml) ÷ 1,000

ABV is the percentage figure printed on the label — 5.0 for a typical lager, 12.0 for table wine, 40.0 for whisky or gin. Volume is the size of the pour in millilitres, not the size of the bottle (unless you are drinking the whole bottle). Dividing by 1,000 converts the ABV percentage and millilitre volume into the equivalent number of 10 ml pure-ethanol units, because a 1% ABV drink is by definition 10 ml of ethanol per litre, which is one unit per litre.

That last sentence is worth lingering on. The formula is not a rule of thumb; it is the algebraic definition of an ABV percentage. A 5% ABV drink is 5 ml of pure ethanol per 100 ml of liquid, or 50 ml per litre, or 5 units per litre. Multiply by the actual volume in litres and the units fall out. The divide-by-1,000 in the NHS version simply lets you key the volume in millilitres, which is how drinks are sold and poured in the UK.

One UK unit also corresponds to 8 grams of pure ethanol, because ethanol has a density of about 0.789 g/ml at room temperature and 10 ml × 0.789 = 7.89 grams, rounded to 8 for simplicity. The grams figure is what most epidemiology papers and international comparisons use, which is why the alcohol units calculator reports both the unit count and the equivalent grams of pure alcohol — the same physical drink, expressed in two different units.

Worked example

Take a Friday night with three pints of 5.2% lager and a small glass of red wine.

A UK pint is 568 ml. At 5.2% ABV, one pint is 5.2 × 568 ÷ 1,000 = 2.95 units. Three pints is therefore 8.86 units — round it to 9. A small 125 ml glass of red at 13.5% ABV is 13.5 × 125 ÷ 1,000 = 1.69 units. Adding the wine takes the evening total to 10.55 units, or about 75% of the UK weekly low-risk ceiling consumed in a single sitting. In ethanol terms, that is roughly 84 grams — more than 10 standard UK units of pure alcohol absorbed over the course of an evening.

That last number is what matters for next-morning effects. The liver clears about one unit per hour, so 10.55 units will keep traces of alcohol in the bloodstream for the best part of half a day after the final drink, plus the usual hour or two for the last drink to be fully absorbed. Anyone planning to drive the following morning should treat this as a non-trivial risk: a 10.55-unit Friday evening that finishes at midnight is unlikely to be fully cleared by 9 am, and even small residues can put a driver over the legal limit. The drink-drive maths is a separate problem, but the unit count is the input it begins from.

Use the alcohol units calculator to run the same arithmetic for any combination of drinks. Each drink is treated independently — enter its volume, ABV and quantity, note the unit total, then repeat and add. Common UK pour sizes worth remembering: a pint is 568 ml, a half is 284 ml, a small wine is 125 ml, a standard wine is 175 ml, a large wine is 250 ml, and a UK single spirit measure is 25 ml (35 ml in some venues).

Factors that affect how alcohol affects you

Body weight and composition

Alcohol distributes through total body water, not body fat. A heavier person, or one with more lean mass, has a larger volume to dilute the same dose into, which is why the same number of units produces a lower peak blood alcohol concentration in a 90 kg adult than in a 60 kg one. Women, on average, carry a slightly higher proportion of body fat and a slightly lower proportion of total body water than men of the same weight, which is one of the reasons the 2016 Chief Medical Officers’ guideline equalised the male and female weekly ceiling at 14 units rather than retaining the older 21/14 split — the evidence on long-term risk did not justify a wider gender gap. The BMI calculator and the lean body mass calculator give a rough sense of where you sit on this scale.

Speed of drinking and food in the stomach

The same unit count produces a very different blood alcohol peak depending on how fast it is drunk and what else is in the stomach. Alcohol absorbed on an empty stomach reaches peak blood concentration in roughly 30 to 60 minutes; absorbed with a substantial meal, the peak can take two hours and run 30 to 50% lower at its highest point. The same 6 units drunk in an hour at the bar after work produce a much higher peak than 6 units spread over a three-course dinner. The unit total is identical — the experience is not.

Age and liver function

Liver enzymes that metabolise alcohol (chiefly alcohol dehydrogenase and CYP2E1) work at roughly the same rate in most healthy adults but decline modestly with age, with chronic liver disease, and with certain medications. Older adults often report stronger effects from the same unit total they tolerated easily in their twenties, partly through slower metabolism and partly through a slightly smaller total body water volume. The 14-unit ceiling is a population average; older adults, smaller adults, and anyone on hepatic-metabolised medication usually need to sit some way below it to keep risk at the same level.

Genetics

A common variant of the ALDH2 gene, present in around 40% of people of East Asian descent, produces a less active form of the enzyme that breaks down acetaldehyde — the toxic intermediate between ethanol and the harmless end-products. Carriers experience flushing, nausea and rapid heart rate from small amounts of alcohol and face substantially higher risks of oesophageal and stomach cancer at any given unit intake. The standard UK guideline does not adjust for this, but the underlying risk picture is materially different, and the safe ceiling for ALDH2 carriers is meaningfully below 14 units.

Pregnancy

The UK Chief Medical Officers’ 2016 guideline is unambiguous on pregnancy: the safest approach is to drink no alcohol at all. There is no known safe lower limit during pregnancy, and the formula on this page does not apply — the unit total is not a guide for risk during pregnancy because risk is not zero at any intake. Anyone pregnant or planning a pregnancy should treat the calculator as informational only and follow NHS pregnancy guidance.

How to stay within the UK low-risk guideline

• Count by units, not by drinks. A pint of modern craft lager at 6% is nearly twice as strong as a half of bitter at 3.6%, yet both count as “one drink”. Convert everything to units using the alcohol units calculator and the league table sorts itself out. Most people who start counting find the running total is higher than they would have guessed.
• Spread units across the week. The 2016 guideline does not just cap the weekly total at 14 units; it explicitly recommends spreading drinking over three or more days and keeping several alcohol-free days per week. Eight units on a Saturday plus six on a Sunday is the same arithmetic as two units across seven evenings but carries a noticeably higher risk profile, particularly for liver and cardiovascular outcomes.
• Watch the home pour. A “glass of wine” poured at home is often 200 to 250 ml rather than the 125 or 175 ml pour you would receive in a pub. A bottle of 13% wine is 9.75 units; pouring it across three home glasses puts each glass at 3.25 units, twice the 1.6 units in a pub small. The label tells you the ABV; only your pour decides the volume.
• Set a hard upper bound for any single session. The CMO guideline notes that drinking more than 6 units (for women) or 8 units (for men) in a single session sharply increases short-term risk — falls, accidents, injuries, alcohol poisoning — regardless of the weekly total. Two evenings of 7 units carry less acute risk than one evening of 14, even with the same weekly figure.
• Hydrate and eat alongside. Alternating alcoholic drinks with water slows absorption, lowers the peak blood concentration, and helps offset the diuretic effect of ethanol that drives most of a hangover’s unpleasantness. Food in the stomach has the same flattening effect.
• Use the percentage-of-limit figure as a check, not a target. The alcohol units calculator shows your total as a percentage of the 14-unit weekly ceiling. That is a low-risk ceiling, not a recommended intake. There is no level of alcohol consumption with zero risk; the lower the running total, the lower the risk.

Common mistakes

Confusing strong drinks with weak ones

A 568 ml pint at 3.6% is 2.04 units; the same pint at 6.5% is 3.69 units. Drinkers who shift from mainstream lagers to craft IPAs without changing their weekly count can double their actual intake while believing it has stayed flat. The ABV is on the label for a reason; check it once per brand and remember the number.

Counting a bottle as one unit, or one drink as one unit

A 750 ml bottle of 13.5% wine is 10.1 units, not one. A single 25 ml shot of 40% spirit is one unit; a 35 ml shot of the same spirit is 1.4 units; a double 50 ml shot is 2 units. “One drink” is a social unit, not an alcohol one, and the two diverge sharply as soon as ABV and pour size start moving around.

Forgetting that cocktails contain multiple units

A standard old-fashioned with 60 ml of 45% bourbon is 2.7 units before any modifier is added. A negroni with 30 ml each of gin, vermouth and Campari at 40%, 16% and 24% respectively totals 2.4 units. Long drinks with a single 25 ml measure sit closer to one unit; short, spirit-forward cocktails routinely deliver three or more units in a single glass and behave nothing like the pint they replace at the same price.

Trusting next-morning recall

Most over-the-limit weekly totals come from under-counting on Saturdays and Sundays, not from deliberate intent. Logging units as you go — in a notes app, in a drink-tracking app, or by re-running the alcohol units calculator for each round — routinely produces higher and more honest weekly totals than reconstructing the weekend on Monday morning.

When to seek professional advice

The unit calculation is arithmetic; the decisions it should prompt are not. Talk to your GP, NHS 111, or a service such as Drinkline (0300 123 1110) if any of the following apply:

• You routinely drink more than 14 units a week and would like support to reduce.
• You drink to manage anxiety, sleep, low mood, or physical pain, or notice withdrawal symptoms (tremor, sweating, restlessness) on days you do not drink.
• You are pregnant, planning a pregnancy, or breastfeeding. The NHS guidance is no alcohol; the unit calculator is informational only in this context.
• You take prescribed medication. Many common drugs (paracetamol, antidepressants, anti-coagulants, some antibiotics) interact with alcohol in ways the unit count alone does not capture.
• You have, or have had, liver, pancreas, or cardiovascular disease, where the threshold at which alcohol becomes harmful is well below the general 14-unit ceiling.

Frequently asked questions

What is the formula for UK alcohol units? Units = ABV percentage × volume in millilitres ÷ 1,000. A 568 ml pint at 5% is 5 × 568 ÷ 1,000 = 2.84 units. The NHS, Drinkaware and the Chief Medical Officers’ guidelines all use this formula. It works for any drink: beer, wine, spirits, cider, cocktails and pre-mixed drinks. A unit corresponds to 10 ml or 8 g of pure ethanol.

How many units are in a pint of lager? It depends on the strength. A 568 ml UK pint at 3.6% ABV (typical bitter or low-strength lager) is about 2 units. A pint at 5% (Stella, Heineken, Foster’s and most mainstream brands) is 2.84 units. A pint at 5.6% (Carlsberg Special Brew, many craft IPAs) is about 3.2 units. Anything above 6% pushes a single pint past 3.4 units.

How many units are in a glass of wine? A 125 ml small glass of 12% wine is 1.5 units. A 175 ml standard glass of 12% is 2.1 units. A 250 ml large glass of 13% wine is 3.25 units — a third of a bottle in one pour. A full 750 ml bottle of 13.5% wine is 10.1 units, so two people sharing it take 5 units each. Stronger fortified wines push these figures up by a fifth or more.

What is the UK weekly limit for alcohol? The Chief Medical Officers’ Low Risk Drinking Guideline, published in 2016, is no more than 14 units a week on a regular basis. This applies to both men and women — the older gendered guidance was dropped after evidence showed similar long-term risks at lower thresholds for both sexes. The guideline also recommends spreading drinking across three or more days and keeping several alcohol-free days per week. There is no level of alcohol consumption that is completely safe; 14 units is a low-risk ceiling, not a target.

How long does alcohol take to leave the body? The liver clears roughly one unit per hour for an average adult, varying with body size, sex, age and liver health. Three pints of 5% lager (about 8.5 units) takes around 8 to 9 hours to fully metabolise, which is why drinking late into the evening can leave residual alcohol in the bloodstream the next morning — a real consideration for drivers. The unit total is the input the morning-after calculation works from: 6 units ≈ 6 hours, 12 units ≈ 12 hours, plus an hour or two for the last drink to be absorbed.

Are UK units the same as US standard drinks? No. A UK unit is 8 g (10 ml) of pure ethanol. A US standard drink is 14 g (17.7 ml), so roughly 1.75 UK units. An Australian standard drink is 10 g, very close to but not identical to a UK unit. EU countries vary between 8 g (Netherlands, Austria) and 14 g (Italy). Always use the UK definition when comparing intake against UK guidance, and check the local definition when reading research published elsewhere.

Does the UK low-risk guideline change with age? Officially, no — the 14-unit ceiling applies to all adults. Practically, older adults often tolerate alcohol less well: liver enzyme activity declines modestly with age, body water volume falls, and polypharmacy is more common. NHS guidance for adults over 65 suggests treating the 14-unit figure as an upper bound, not a target, and aiming materially lower. The calculator gives the same number regardless of age; the interpretation is the part that should adjust.

Is there a safe number of units in pregnancy? The 2016 UK Chief Medical Officers’ guideline states that no level of alcohol consumption is known to be safe in pregnancy and that the safest approach is not to drink at all while pregnant or trying to conceive. The unit calculator on this page is informational only in a pregnancy context; the figure it returns is not a safety margin, because there is no established safe lower limit.

Related calculators

Use these alongside the alcohol units calculator to build a fuller picture of diet, health, and lifestyle.

• BMI calculator — body mass index with WHO categories, a population-level screen for weight-related risk that pairs naturally with alcohol intake when reviewing overall health.
• BMR calculator — basal metabolic rate for daily calorie planning. Alcohol adds about 7 kcal per gram, or 56 kcal per UK unit, on top of food calories — a bottle of wine is over 600 kcal before the food it is drunk with.
• Calorie calculator — maintenance, cut and bulk targets. Alcohol calories are routinely under-counted in weight-loss plans; running them through here is the simplest way to see how much of a deficit they eat into.
• TDEE calculator — total daily energy expenditure, the figure to eat to in order to maintain weight. Combined with the unit count, it shows how much alcohol fits into a given calorie budget before it starts to drive a surplus.