What is a unit of alcohol?

There are so many serious health and social complications of drinking excess alcohol, that it was necessary to bring out and recommend safe drinking limits for men and women. Alcohol units have been referenced to define the safe limits of drinking alcohol in a man or woman.

The idea of including alcohol units was first introduced in the United Kingdom in 1987 to help people keep a watch on their drinking levels. Units simply express the quantity of pure alcohol in a drink.

A unit of alcohol is 10ml of pure ethanol, near enough to 8g of alcohol (equivalent to 10 mL of pure ethanol).

The number of alcohol units in a drink depends on the size of the drink and the amount of pure alcohol in it. For example, a pint of strong beer contains 3 units of alcohol, whereas the same volume of mild beer has a little over 2 units.

How much is a pint?

  • The British imperial pint is 568 ml
  • The US liquid pint is  473 ml
  • In many metric countries, it is a half-liter or 500 ml

Knowing the safe number of units that you should consume per day or per week will help you control your drinking and stay within the safe healthy limits.

How much is a unit of alcohol?

An average healthy adult can metabolize one alcohol unit in one hour. Alcohol units vary from country to country. In the United Kingdom, one unit of alcohol is equivalent to 10 ml of pure alcohol by volume or 8 grams of pure alcohol by weight.

In everyday life, one alcohol unit is equal to about:-

  • A half-pint of mild-strength beer (4% by volume)
  • 25 ml of whiskey of 40% alcohol by volume
  • 50 ml of fortified red wine such as port or sherry of 20% alcohol by volume

However, stronger alcoholic beverages by volume percentage than the above are available and consumed. In such cases, a simple formula is to calculate the number of units of alcohol you have consumed:

Formula to calculate alcohol units in your drink

Alcohol by volume (ABV) is a standard measure of the amount of pure alcohol (ethanol) as a percentage of the total volume of liquid in a drink. You will find it expressed on the labels of cans and bottles of the alcoholic beverage as “vol” or “alcohol volume”.

You can calculate the number of alcoholic units in any alcoholic drink by multiplying the strength of the alcoholic beverage (ABV) with the volume of the drink consumed (in milliliters) and then dividing the product by 1000.

  • ABV x volume of drink ÷ 1,000 = alcoholic units

For example, if you have drunk one liter of strong beer of 6% alcohol by volume, then your consumed units will be 6 x1000 ÷ 1000 = 6 alcohol units.

Recommended alcohol units per day

The government of the U.K. has advised the following safe limits of drinking alcohol for regular drinking:

  • 3 to 4 units a day for men, that is about a 1 and a half-pint of 4% beer or about 90 ml (one and a half peg) of 40% whiskey.
  • 2 to 3 units a day for women, that is about 175 ml glass of 13% wine.
  • Recommendations for pregnant women: Pregnant women, at best should abstain from drinking alcohol, though previously light drinking was allowed as it would not pose any health risks or cause alcohol fetal syndrome. Light drinking would mean one to two units, not more than once or twice a week. However, this recommendation is withdrawn and now pregnant women are advised to abstain from drinking alcohol altogether.

Recommended alcohol units per week are now 4 units

Previously, prior to 2016, the guidelines were as follows:

  • Men should not drink more than 21 alcohol units per week. It does not mean you can drink 21 units once a week. These per week recommendations are to be spaced out and should not exceed 4 units  per day.
  • Recommended alcohol units per week for women are 14 units, which you should space out throughout the week.

However, in 2016, the British government updated the alcohol guidelines in the UK after nearly two decades.

The UK’s chief medical officers reduced the recommended maximum number of units to 14 per week for both men and women. The previous recommendation of 21 units per week for men was withdrawn.

Safe units of drinking alcohol before driving

It is strongly recommended that one should never drink before or while driving. However, circumstances may force one and the U.K. government has provided the following safe drinking limits before driving.

  • Men should not drink more than four units of alcohol before driving.
  • Women should not drink more than three units of alcohol before driving.
  • If you have to drive the next day in the morning,  men should not drink more than 10 alcohol units the previous night, and
  • Women should not drink more than seven units the previous night if they have to drive the next day in the morning.