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How Much is a Unit of Alcohol?

How to calculate a Unit of Alcohol

Confused about how much exactly is a unit of alcohol? So was I, until I did some research and came up with some formulae.

1 Unit = 10ml of pure alcohol.

For an easy calculation, we can multiply the percentage of alcohol by volume (the ABV%) by the volume in litres, as follows:

ABV% x Litres = Units

As an example for strong red wine.
13 (ABV%) x 0.175 (large glass or 1/4 bottle) = 2.3 Units.

As an example for weaker wine.
9 (ABV%) x 0.175 (large glass or 1/4 bottle) = 1.6 Units.

As an example for a pint of beer.
4.2 (ABV%) x 0.568 (0.568 litres is a pint) = 2.4 Units.

As an example for a small bottle of strong lager.
5 (ABV%) x 0.284 (bottle sizes vary) = 1.4 Units.

As an example for a large can of weak beer or lager.
2.8 (ABV%) x 0.440 (large can) = 1.2 Units.

As an example for a single shot of spirit.
40 (ABV%) x 0.025 (single shot UK) = 1 Unit.

Size and Strength Matters

The strength of alcoholic beverages vary, as will the size of the container, which is why the generic guidelines of “How many units in a glass of wine beer or a cocktail?” cannot work and can only ever be used as a rather vague guide

What about working it back the other way?

What if I want to pour myself say one unit (of alcohol) of my favourite drink?

You will need to know the ABV% (you will also need a measuring jug).

1 / ABV% = Quantity (litres per unit)

As an example for strong red wine.
1 / 13 (ABV%) = 0.077 litres for 1 Unit.

As an example for weaker wine.
1 / 9 (ABV%) = 0.111 litres for 1 Unit.

As an example for beer.
1 / 4.2 (ABV%) = 0.238 litres for 1 Unit.

As an example for strong lager.
1 / 5 (ABV%) = 0.200 litres for 1 Unit.

As an example for weak beer or lager.
1 / 2.8 (ABV%) = 0.357 litres for 1 Unit.

As an example for full strength spirits.
1 / 40 (ABV%) = 0.025 litres for 1 Unit.

All the above measurements are in litres.
For pints or fluid ounces use the following conversion rates:
Litres to pints x 1.76
Litres to fl. oz. x 35.2

A Safe Consumption for Health

Current guidelines for safe consumption is 21 units per week for men and 14 units per week for women. [updated January 2016 to 14 units per week for both sexes.] With no more than 4 (men) and 3 (women) units in any one day, plus two alcohol-free days per week. Pregnant women and women trying to conceive should not drink alcohol at all.

Drinking and Driving

There is no clear cut advice on drinking and driving apart from don’t drink and drive. However it is generally thought that 4 units (men) and 3 units (women) will not take you over the UK limit of 80 milligrams of alcohol in every 100 millilitres of blood (Scotland is 50 milligrams of alcohol in every 100 millilitres of blood and is therefore less). But it should be noted that drinking up to the limit is a risky strategy for both safety and staying within the law, as we all absorb and process alcohol differently and body size makes a difference too. Therefore if you do have the odd drink and then later intend to drive, it is important to stay well below the 4 or 3 units suggested, if you want to stay safe and be within the law.

Alcohol Level Reduction Time

It is also generally accepted that the alcohol level reduces in our system at the rate of 1 unit per hour, after an initial hour. So if your daily alcohol intake high, it is quite possible that you will never be fit to drive (you may also want to consider whether you have a ‘drink problem’ and how much your alcohol intake could be affecting your general health).

This article is written for general information only and should not be relied on. I am not a doctor, nor a health professional, nor a legal advisor, heck, I am not even a mathematician (perhaps just a little OCD when it comes to figures).