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Counting alcohol units – ask Decanter

Our expert talks through the intricacies of alcohol units and how they equate to a glass of wine.

Understanding Alcohol Units

Joyce Jones, Birmingham, asks: Is an alcohol unit the same in the UK as it is in the US or Europe, and what is the difference between a unit of wine and a unit of spirits? Am I better off having a shot of vodka, for example, than a glass of wine?

Michael Apstein MD replies:

The British government introduced the concept of a ‘unit of alcohol’ in 1987 as a way for individuals to measure the amount they consume because wine, spirits and beer vary in the amount of alcohol they contain.


One unit of alcohol equals 10ml

  • 175ml of wine at 12% ABV – 2.1 units
  • 175ml of wine at 15% ABV – 2.6 units
  • 250ml of wine at 12% ABV – 3 units
  • 250ml of wine at 15% ABV – 3.75 units
  • 25ml shot of 40% ABV Vodka – 1 unit
  • Pint (568ml) of 4.8% ABV lager – 2.7 units

A 250ml glass of 13% white wine has more alcohol units than three 25ml vodka shots

One unit of alcohol equals 10ml, or 8g, of pure alcohol whether it comes from wine, spirits or beer.

It’s a way of standardising the playing field because a ‘glass of wine’ or ‘a shot’ is an imprecise measurement.

For example, a standard glass (175ml) of Chablis (12% alcohol by volume) contains about two units (175ml x 0.12 = 21ml of pure alcohol or 2.1 units), whereas a bigger glass (250ml) – but still ‘a glass’ – of 15% abv Australian Shiraz contains almost twice as much (3.75 units).

Similarly for spirits, it depends on the size of the shot. In England and Wales, one shot is 25ml, whereas, in Scotland and Northern Ireland a standard shot is 35ml. Hence, a shot of vodka (40%abv) in London has one unit of alcohol, but in Edinburgh it has almost 1.5.

So if by ‘better off’, you mean what is potentially less harmful between a glass of wine or a shot of vodka, then it depends on the size of the glass or shot, what you mix the vodka with, over what period of time you drink them, whether you eat or not, and, of course, your overall health.

UK government guidance on drinking introduced in January 2016 said that no one should exceed 14 units per week.



The USA have health guidelines in based on the Standard Drink measure which can be used to benchmark alcoholic drinks in the same way as the UK. In the US, the measurement changes with one unit of alcohol being 14g of pure alcohol or 5 fl. oz. It is used as a guideline for how many drinks a day you can consume, as well as for other alcohol related health measures.

Source: U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015 – 2020 Dietary Guidelines for Americans

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