What is an alcohol unit?

Understanding how many units of alcohol you drink is a great first step to looking after your health and wellbeing. But what is a unit, and what does it mean?

What is an alcohol unit?

Alcohol units are a simple way of understanding the quantity of pure alcohol in a drink.

One unit is 10ml or 8g of pure alcohol.¹ Because alcoholic drinks come in different strengths and sizes, units are a way to tell how strong your drink is, which can also help you to make comparisons.

As an example, a pint of 3.8% ‘alcohol by volume’ or ABV beer – see below for explanation – has just over two units, while a single measure (25ml) of typical spirits is one unit.²

It takes an average adult around an hour to process one unit of alcohol so that there's none left in their bloodstream, although this varies from person to person.³ And the more you drink, the longer it takes – so, six units of alcohol would take the average person six hours to process.

The UK’s Chief Medical Officers advise that, if you choose to drink, it’s safest to drink no more than 14 units a week (for both men and women). It’s also important to spread any drinking over three or more days, with several drink-free days, and no bingeing.⁴

Alcohol by volume

Drinks labels contain information on the percentage of alcohol a drink contains – this is known as ‘alcohol by volume’ or ABV.

Look on a bottle of wine or a can of lager and you'll see either a percentage, followed by the abbreviation ‘ABV’, or sometimes just the word ‘vol’. So, as an example, wine that says ‘13 ABV’ on its label contains 13% pure alcohol.

The alcoholic content of similar types of drinks can vary a lot. For example, some ales are 3.5% ABV, but stronger continental lagers and craft beers can be 5% or 6% ABV, or even more – always check the label.

The same is true for wine – some stronger wines can exceed 14% ABV. The only way to be sure of how much alcohol is in your glass of wine is to check the label or ask at the bar.

One pint of strong lager (5.2% ABV) or a large glass of wine (14% ABV) contain more than three units of alcohol.⁵

Spirit measures and wine glass sizes

Pubs and bars usually serve spirits (like vodka, gin, rum or whisky) in 25ml measures – about one unit of alcohol, or ‘doubles’ which is a 50ml measure and about two units of alcohol.

Wine sold in licensed premises have to offer either 125ml, 175ml, or 250ml glasses. Or by the bottle (750ml).⁶ If you order a large glass of wine (14% ABV), that means you’re having 250ml – and that is likely to contain three and a half units of alcohol in a single glass.⁷

So, drinking three large glasses of wine is the same as drinking a whole bottle (750ml), which, like any binge drinking, can have serious consequences for your health. Binge drinking is defined as drinking more than eight units of alcohol in a single session for men and more than six units of alcohol in a single session for women.⁸

Regularly having just one or two heavy drinking episodes a week will increase your risk of death from long-term illness and from accidents and injuries.⁹

Switching to a smaller wine glass or a bottle of beer instead of a pint can help reduce the amount of units you drink. The Chief Medical Officers’ advise that you can reduce your risks by limiting the total amount of alcohol you drink on any single occasion, drinking more slowly, drinking with food, and alternating with water.¹⁰

If you drink at home, a good way to avoid accidentally pouring too much and limit how many units of alcohol you have is by tracking your drinks using a unit measuring cup.