What a Standard Drink Actually Is

A standard drink is a mass, and you can compute it

Every national definition of a standard drink is a quantity of pure ethanol, so the calculation is the same everywhere: take the volume in millilitres, multiply by the alcohol by volume expressed as a fraction, and multiply by 0.789 g/ml, the density of ethanol at room temperature. That gives grams of ethanol, and grams of ethanol is the only quantity that is genuinely comparable between a beer, a glass of wine and a shot of spirits.

The formula is easy to verify against a published definition. NIAAA describes one US standard drink as 5 fluid ounces of table wine at 12% ABV. Five fluid ounces is 147.87 ml, so 147.87 × 0.12 × 0.789 = 14.00 g — exactly the 14 g NIAAA states. Run the same check on its other two examples and both land on 14.00 g: 12 fluid ounces of 5% beer, and 1.5 fluid ounces of 40% spirits. The definitions are internally consistent, which means the formula reproduces them rather than approximating them, and you can apply it with confidence to whatever is actually in your glass.

The mass changes at the border

There is no international standard drink. Kalinowski and Humphreys surveyed governmental definitions in 37 countries and found no agreement on the number, and the markets covered here span most of the range on their own. NIAAA sets the US figure at 14 g. The NHS defines a UK unit as 10 ml of pure alcohol, about 8 g. Santé publique France, Spain's Ministerio de Sanidad and Portugal's SICAD all use 10 g. Italy's Istituto Superiore di Sanità uses an unità alcolica of 12 g, and German guidance from the Bundeszentrale für gesundheitliche Aufklärung describes a Standardglas of roughly 10 to 12 g. Between the smallest and the largest there is nearly a factor of two.

The British definition is worth a closer look, because it is the only one of the group specified as a volume rather than a mass. One unit is 10 ml of pure ethanol; at 0.789 g/ml that is 7.89 g, which is why the NHS describes it as "about 8 g". The practical NHS formula, units = millilitres × ABV ÷ 1,000, follows directly from the volume definition and is the one to use in the UK. It also produces some pleasing coincidences: a 25 ml pub measure of 40% spirit is exactly one unit, and a 250 ml glass of 13% wine is exactly 3.25.

One glass, several right answers

Pour 175 ml of a 13% wine — a common restaurant measure and a modest glass by any domestic standard. The ethanol is 175 × 0.13 = 22.75 ml, and 22.75 × 0.789 = 17.95 g. That number is a physical fact about the liquid and does not change when you cross a border. What changes is the denominator. Divide by 14 and you have 1.28 US drinks. Divide by 10 ml and you have 2.28 UK units. Divide by 10 g and you have 1.79 French, Spanish or Portuguese units. Divide by 12 g and you have 1.50 Italian units, or 1.50 to 1.79 German Standardgläser depending which end of the range is being used.

None of those answers is wrong, and the spread between them is not a rounding artefact — 2.28 is 78% more than 1.28 for an identical glass. This is why quoted drinking figures do not survive translation. A survey reporting that respondents average "ten drinks a week" means 140 g of ethanol in the United States and 79 g in the United Kingdom. Whenever you compare two numbers about alcohol, convert both to grams first, because grams is the only quantity that means the same thing on both sides of the comparison.

The pour on your table is not the pour in the definition

Standard-drink definitions describe measured servings. Homes do not use measures. De Beukelaar and colleagues had 201 people in the Netherlands pour as they normally would and then weighed the result: the mean red-wine portion was 131.7 ml and the mean white-wine portion 129.4 ml, against a Dutch standard serving of 100 ml — about 30% over. Fortified wine came out at 94.0 ml against a 50 ml standard, roughly 90% over. Spirits were poured at 47.0 ml against 35 ml. Every category ran high, and the overshoot grew with the strength of the drink.

Put that together with a large modern wine glass and the arithmetic of a quiet evening changes. Two 250 ml pours of a 13% wine — not an extravagant evening by the standards of most dinner tables — is 500 × 0.13 × 0.789 = 51.3 g of ethanol. That is 5.1 French, Spanish or Portuguese units, 6.5 UK units, 4.3 Italian units or 3.7 US drinks. The person who reports "two glasses" is not lying and is not exaggerating; they are using a word that does not mean what the guideline means by it, and the error runs in one direction only.

The calories come from the ethanol, not the sugar

Ethanol is metabolised at 7 kcal per gram — a figure written into European labelling law, in Annex XIV of Regulation 1169/2011, alongside 4 kcal/g for carbohydrate and 9 for fat. Once you know the ethanol mass you already know most of the energy. The 175 ml glass of 13% wine contains 17.95 g of ethanol, which is 17.95 × 7 = 126 kcal before anything else is counted.

The rest is residual sugar, and in dry wine there is very little. A wine with 2 g of sugar per litre contributes 0.35 g in a 175 ml glass, or 1.4 kcal — about 1% of the total, which lands the glass at roughly 127 kcal. Push to an off-dry style at 12 g per litre and the sugar adds 8 kcal, taking the glass to about 134. In other words, choosing a drier wine changes the calorie count by a few per cent, while choosing a smaller pour or a lower ABV changes it in proportion. If the calories are the concern, the lever is the ethanol, and the ethanol is volume times strength.

Guideline numbers do not travel either

Because the unit differs, the guidance expressed in units differs too — and not by as much as it looks. The UK Chief Medical Officers advise no more than 14 units a week, which at 10 ml each is 140 ml of ethanol, or 110 g. Santé publique France advises no more than 10 glasses a week, at 10 g each, so 100 g. Written as "14" against "10", the British figure looks 40% more permissive. Converted to grams, it is about 10% more. Almost the whole apparent gap is a unit conversion pretending to be a policy difference.

The United States has moved in a different direction. The 2025–2030 Dietary Guidelines for Americans, published in January 2026, dropped the previous numeric caps of two drinks a day for men and one for women and replaced them with advice to consume less alcohol for better health, without stating a limit. The standard drink of 14 g remains defined by NIAAA, so American drinkers still have a unit — they simply no longer have a federal number to measure it against. Nothing in that change affects the arithmetic on this page: whatever guidance you follow, the way to apply it is to convert your own drinks into grams of ethanol first.

What the unit does not tell you

A unit is a measure of quantity, not of effect. The same 17.95 g of ethanol produces a different blood alcohol concentration in different people, because that depends on body water, sex, food in the stomach and the rate at which the drink went down — none of which appears in a standard-drink figure. Two people can drink identical amounts, count identical units, and be in materially different states an hour later. Counting units tells you what you consumed. It does not tell you what it did.

It is also worth being plain about what the unit is for. National definitions exist so that surveys, research and public guidance can use a common yardstick within one country — not so that a number can be declared safe. Health authorities across these markets are explicit that there is no threshold below which alcohol carries no risk, and the trend in recent guidance has been to lower the stated figures or, in the American case, to drop them. The calculator on this site converts drinks into grams accurately. Deciding what to do with that number is a matter for you, and where it matters, for your doctor.

Frequently asked questions

How do I work out the units in any drink myself?

Multiply the volume in millilitres by the ABV as a fraction, then by 0.789 to get grams of ethanol, then divide by your market's standard. A 330 ml beer at 5% is 330 × 0.05 × 0.789 = 13.0 g, which is 0.93 US drinks, 1.30 French or Spanish units, 1.09 Italian units and 1.65 UK units.

Why is a UK unit smaller than a US standard drink?

Because the two countries picked different masses. The UK unit is defined as 10 ml of pure ethanol, which weighs 7.89 g; the US standard drink is 14 g. One US drink is therefore about 1.8 UK units, which is why a British weekly figure and an American daily figure cannot be compared without converting both to grams.

Is a 175 ml glass of wine "one glass"?

In everyday speech yes, in the arithmetic no. At 13% it holds 17.95 g of ethanol, which is 1.79 standard units in France, Spain or Portugal, 1.50 in Italy and 2.28 in the United Kingdom. Only in the United States, where the standard is 14 g, does it come close to one — and even there it is 1.28.

Do the calories in wine come from the sugar or the alcohol?

Almost entirely from the alcohol. Ethanol is 7 kcal per gram, so the 17.95 g in a 175 ml glass of 13% wine is 126 kcal. A dry wine at 2 g of residual sugar per litre adds only 1.4 kcal to that glass — about 1% of the total. Reducing the pour or the strength moves the number; choosing a drier style barely does.

One guideline says 14 a week and another says 10. Which country is stricter?

Convert before judging. Fourteen UK units at 10 ml each is 140 ml of ethanol, about 110 g. Ten French glasses at 10 g each is 100 g. The written figures differ by 40%, the actual quantities by about 10%. Almost the whole gap is the unit, not the policy.

Does counting units tell me whether I am safe to drive?

No. A unit measures how much ethanol you drank, not the concentration in your blood, which depends on body water, sex, stomach contents and how quickly you drank. Legal limits differ by country and by licence class, and no calculator can certify you are under one. If you have been drinking, do not drive.