Alcohol units and standard drinks

How to calculate the alcohol in a serving

Start with the serving volume and alcohol by volume, or ABV. A 500 ml beer at 5% ABV contains 25 ml of pure alcohol. That equals 2.5 UK units, but the standard-drink result is different under definitions based on grams. Check the label and serving size because venue measures, cans and glasses vary.

Use the free alcohol units and standard drinks calculator to choose a national definition and total one serving or several drinks.

Why the national definition matters

The NHS explains UK units, the US National Institute on Alcohol Abuse and Alcoholism explains US standard drinks, the Australian Government explains Australian standard drinks, and the Canadian Centre on Substance Use and Addiction explains the Canadian definition. These measures help compare servings, but lower-risk guidance also varies by country and can change. Check current official advice where you live.

Alcohol measures cannot assess impairment or give permission to drive. Read why a calculator cannot tell you if you can drive.

UK units and standard drinks compared

The same 500ml beer at 5% ABV contains 25ml of pure alcohol. The number you record changes with the national definition, even though the beer itself has not changed.

These totals are rounded to one decimal place. For the definitions expressed in grams, the example uses 0.789g of ethanol per millilitre, as our calculator does. A smaller number in a different system does not mean less alcohol or less risk. Do not compare a UK unit total directly with guidance expressed in US standard drinks.

Choose the right calculator setting

1. Select the country whose alcohol guidance you are using. The calculator starts with UK units, so change the definition if needed.
2. Enter the amount you drink and the ABV shown on the label. If a bottle is shared, use your portion rather than the whole bottle.
3. Keep that definition for every entry in the total. When comparing a drink label with a calculator result, check which country's definition the label uses.

Compare your serving in the alcohol calculator. For a plan that also covers time and transport, read how to plan a night out.

Why a drink count can mislead

• A double spirit is still one glass but contains twice the measure.
• A strong craft beer may contain far more alcohol than a lower-strength lager of the same size.
• A large wine glass may hold more than one standard serving.
• Cocktails can contain several measures without making that obvious.

Use one consistent definition

A night-out drink limit can support an immediate plan, while units or standard drinks can help you compare servings over time. Do not mix national definitions in one total. None of these numbers can calculate impairment or tell you whether driving is safe. Medication, health conditions and pregnancy can also change what advice applies, so use professional guidance where relevant.