What Is a Standard Drink?
A standard drink is a fixed amount of pure alcohol, and the amount differs by country: 8 g in the UK, 10 g in Australia, 14 g in the US.
In short
A standard drink is a unit for counting alcohol, defined as a fixed mass of pure ethanol, and the mass varies by country. A UK unit is 8 grams, an Australian standard drink is 10 grams, and a US standard drink is 14 grams. So one US drink is nearly two UK units, and drinking guidelines from different countries cannot be compared without converting first.
The term sounds universal and it is anything but. A standard drink is a counting unit for pure alcohol, and different countries have chosen different amounts, which means a glass of wine is one drink in one country and nearly two in another.
The definitions
| Country | Standard drink |
|---|---|
| United Kingdom | 8 g (1 unit) |
| Australia, New Zealand, much of Europe | 10 g |
| Canada | 13.5 g |
| United States | 14 g |
| Japan | about 20 g |
The grams refer to pure ethanol. Ten millilitres of ethanol weighs about 8 grams, which is where the UK figure comes from.
What that means in the glass
A 175 ml glass of 13 percent wine contains about 18 g of alcohol. That is 2.3 UK units, 1.8 Australian standard drinks, or 1.3 US standard drinks.
A pint of 5 percent lager contains about 23 g. That is 2.8 UK units, 2.3 Australian drinks, or 1.6 US drinks.
A 25 ml single measure of 40 percent spirit is 8 g: exactly one UK unit, 0.8 Australian, 0.6 US.
Why it matters
Guidelines are written in local units. The US advises up to two drinks a day for men, which is 28 g. The UK advises no more than 14 units a week, which is 112 g, or 16 g a day. An American reading UK advice, or the reverse, without converting will misjudge it by a factor of nearly two.
The same applies to research. A study reporting risk per drink means different amounts depending on where it was done, and popular reporting almost never converts.
Calculating it yourself
Grams of alcohol equals volume in millilitres, times percentage strength, times 0.789, divided by 100. The 0.789 is the density of ethanol.
For a 250 ml glass at 13 percent: 250 × 13 × 0.789 ÷ 100 = 25.6 g, which is 3.2 UK units or 1.8 US drinks.
Divide the grams by your country’s standard to get the drink count.
The drift problem
The UK unit was set in 1987 as the alcohol in a half pint of beer or a single spirit measure. Since then, beer has moved from around 3.5 percent to 4.5 or 5, wine from 11 or 12 percent to 13 or 14, and a standard wine glass has grown from 125 ml to 175 or 250. A “glass of wine” today can carry three times the alcohol of one in 1987, and people who count in glasses are counting a moving target.
That is why the guidance is in units rather than drinks, and why a conversion is worth doing once for the things you actually drink.
Common questions
How many standard drinks are in a bottle of wine?
A 750 ml bottle at 13 percent contains about 78 grams of alcohol, which is 9.75 UK units, about 7.7 Australian standard drinks, or about 5.5 US standard drinks. Same bottle, three different counts.
Why does the UK use such a small unit?
The 8 gram unit was set in 1987 as the alcohol in a single 25 ml measure of 40 percent spirits, or half a pint of ordinary-strength beer at the time. Beer and wine have both become stronger since, so those equivalences no longer hold.
What is the safest number of drinks a week?
UK guidance says no more than 14 units, spread over three or more days. The World Health Organization's position is that no level is entirely safe for health. Both agree that spreading intake and having drink-free days lowers risk.
Sources
Every factual claim above traces to one of these. Follow them rather than taking this article's word for it.
- Calculating alcohol units NHS
- Alcohol consumption: advice on low risk drinking UK Chief Medical Officers
- No level of alcohol consumption is safe for our health World Health Organization
Try it yourself
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