Standard Drink Alcohol Units

The divisor is set by the definition of the standard drink in each country. The formula (mL × ABV%) / 1000 works because 1000 mL × 1% ABV = 10 mL of pure alcohol = 1 UK unit. If your country defines a standard drink as 14 g (as in the US), the divisor is different because 14 g ÷ 0.789 g/mL = 17.74 mL, so the formula becomes U = (mL × ABV%) / 1774. If your country uses 10 g (Australia), the divisor is 10 g ÷ 0.789 = 12.67 mL, so U = (mL × ABV%) / 1267. This calculator uses the UK divisor of 1000, and shows the US and Australian equivalents in the companion metrics. The physical drink is the same in all cases — only the number attached to it changes.

It depends on the ABV. A UK imperial pint is 568 mL. At 4% ABV, that is (568 × 4) / 1000 = 2.27 units. At 4.5% it is 2.56 units. At 5.2% — the strength of many standard lagers — it is 2.95 units, close to three. At 6% (a strong ale or IPA) it is 3.41 units. The old rule of thumb that "a pint is two units" comes from the era when most British beer was around 3.5% ABV, which gives 1.99 units — almost exactly two. Modern beer is stronger on average, and craft beers routinely exceed 6%, so the same glass now contains substantially more alcohol than the traditional rule suggests. This is why checking the ABV on the pump clip or can matters more than counting pints.

Yes, measurably. A study published in the BMJ in 2017 analysed the capacity of wine glasses in England from 1700 to the present and found that the average wine glass has grown from about 66 mL in 1700 to around 450 mL today — nearly a sevenfold increase. Restaurant and bar serves have grown alongside: the "medium" glass in most UK pubs and restaurants is now 175 mL (2.1 units at 12%), while a "large" glass is 250 mL (3.0 units). A single large glass of wine therefore contains more alcohol than the NHS's recommended daily limit of 2 units, and two large glasses exceed the entire weekly guideline in one sitting. The glass size effect is one of the strongest environmental drivers of unintentional heavy drinking.

A healthy adult liver metabolises roughly one UK unit (7.89 g) per hour — about 8–10 g of ethanol per hour for men, and slightly less for women. This rate is essentially fixed: it cannot be accelerated by coffee, cold showers, exercise, food, or water. Only time reduces blood alcohol concentration. This is why the "one unit per hour" rule is used throughout this calculator: a drink containing 2.1 units will take roughly two hours and ten minutes to fully metabolise. If you drink faster than that, alcohol accumulates in the blood. The rate is slower in people with liver disease, and can be affected by medications that compete for the same CYP2E1 and ADH pathways, including some antibiotics, painkillers, and antidepressants. It is also slower when the stomach is empty, because alcohol is absorbed faster without food to slow gastric emptying.

The UK Chief Medical Officers' guideline, revised in 2016, states that both men and women should drink no more than 14 units per week — the same for both sexes, ending the previous sex-specific limits. The guideline recommends spreading those 14 units evenly over three or more days rather than saving them for the weekend, and defines a "binge" as drinking more than 6 units (women) or 8 units (men) in a single session. The guideline also states that there is no "safe" level of drinking and that the recommended limit is a low-risk level, not a target. For pregnant women, and for anyone under 18, the recommended amount is zero. For anyone taking medication that interacts with alcohol, driving, or operating machinery, the guidance is also zero for those specific activities.

This is the position of the World Health Organization as of 2023: no level of alcohol consumption is completely safe, because even light drinking is associated with a small but measurable increase in the risk of certain cancers (particularly breast, colon, liver, and oesophageal) and cardiovascular events. The WHO's statement followed decades of epidemiological work — including the Global Burden of Disease studies — that found the protective effect of moderate drinking on cardiovascular disease is smaller than previously believed, and is outweighed by increased cancer risk even at low levels. Individual national guidelines vary in how they express this. The UK's 2016 guideline says "there is no safe level", while still providing a low-risk threshold of 14 units per week. Canada went further in 2023 and reduced its guidance to just 2 drinks per week. The practical takeaway is that "low risk" and "no risk" are different things, and each guideline represents a country's judgement about the level of risk it considers acceptable.

The formula is exact for any drink where you know the volume and the ABV — which is straightforward for a single ingredient like a can of beer or a glass of wine, but less so for a mixed cocktail, because the final ABV of a mixed drink depends on the ratio of spirit to mixer. A margarita made with 50 mL of 40% tequila, 25 mL of triple sec (about 30% ABV), and 25 mL of lime juice has a total volume of 100 mL and contains 50 × 0.40 + 25 × 0.30 + 25 × 0.00 = 20 + 7.5 + 0 = 27.5 mL of pure alcohol, giving a final ABV of about 27.5% and 2.75 UK units. The mixers can be deceptive: a cocktail served in a tall glass with lots of juice or soda can look like a soft drink but contain two or three spirits' worth of alcohol. The rule of thumb is to count spirits rather than volume: one 25 mL shot of 40% spirit = 1 unit, so a cocktail with three shots contains about 3 units regardless of how much mixer was added.