A standard drink or (in the UK) unit of alcohol is a measure of alcohol consumption representing a fixed amount of pure alcohol. The notion is used in relation to recommendations about alcohol consumption and its relative risks to health. It helps to educate alcohol users.^[1] A hypothetical alcoholic beverage sized to one standard drink varies in volume depending on the alcohol concentration of the beverage (for example, a standard drink of spirits takes up much less space than a standard drink of beer), but it always contains the same amount of alcohol and therefore produces the same amount of drunkenness.^[1] Many government health guidelines specify low to high risk amounts in units of grams of pure alcohol per day, week, or single occasion. These government guidelines often illustrate these amounts as standard drinks of various beverages, with their serving sizes indicated. Although used for the same purpose, the definition of a standard drink varies from country to country.

Labeling beverages with the equivalent number of standard drinks is common in some countries.

Definitions in various countries

There is no international consensus on how much pure alcohol is contained in a standard drink;^[2] values in different countries range from 8g to 20g. The example questionnaire form for the World Health Organization's Alcohol Use Disorders Identification Test (AUDIT) uses 10g,^[3] and this definition has been adopted by more countries than any other amount.^[4] Some countries choose to base the definition on mass of alcohol (in grams) while others base the unit on the volume (in mL or other volume units).^[1] For comparison, both measurements are shown here, as well as the number of standard drinks contained in 500 mL of 5% ABV beer (16.9 US fl oz, a typical large size of beer in Europe, slightly larger than a US pint of 473ml). The terminology for the unit also varies, as shown in the Notes column.

Calculation of pure alcohol mass in a serving

In the UK, it is sometimes misleadingly stated that there is one unit per half-pint of beer, or small glass of wine, or single measure of spirits. However, such statements do not take into account the various strengths and volumes supplied in practice.^[29][30] Such approximations can lead to people underestimating their alcohol intake.^[30] In some countries, the number of units of alcohol in a beverage can instead be read directly on the label.^[31]

In countries without labeling, it is possible to calculate the pure alcohol mass in a serving from the concentration, density of alcohol, and volume:

$${\displaystyle {\text{Pure alcohol mass))={\text{volume))\times {\text{alcohol by volume))\times {\text{density of alcohol))}$$

For example, a 350 ml glass of beer with an ABV of 5.5% contains 19.25 ml of pure alcohol, which has a density of 0.78945 g/mL (at 20 °C),^[32] and therefore a mass of 15.20 grams.

$${\displaystyle 350\,\mathrm {mL} \times 0.055\times 0.78945\,\mathrm {g} /\mathrm {mL} \approx 15.20\,\mathrm {g} }$$

$${\displaystyle 0.35\,\mathrm {L} \times 0.055\times 789.45\,\mathrm {g} /\mathrm {L} \approx 15.20\,\mathrm {g} }$$

The standard UK units of alcohol in a drink can be determined by multiplying the volume of the drink (in millilitres) by its percentage ABV, and dividing by 1000. For example, one imperial pint (568 ml) of beer at 4% alcohol by volume (ABV) contains:

${\displaystyle {\begin{aligned}568{\mbox{ ml))\times 4\%\times {\frac {1{\mbox{ unit))}{10{\mbox{ ml))))&&=&&568{\mbox{ ml))\times {\frac {4}{100))\times {\frac {1{\mbox{ unit))}{10{\mbox{ ml))))&&=&&568{\mbox{ ml))\times {\frac {4{\mbox{ units))}{1000{\mbox{ ml))))&=2.3{\mbox{ units))\end{aligned))}$

The formula uses ml ÷ 1000. This results in exactly one unit per percentage point per litre, of any alcoholic beverage.

The formula can be simplified for everyday use by expressing the serving size in centilitres and the alcohol content literally as a percentage:

${\displaystyle {\begin{aligned}75{\mbox{ cl))\times 12\%\times {\frac {1{\mbox{ unit))}{1{\mbox{ cl))))&&=&&75{\mbox{ cl))\times {\frac {12}{100))\times {\frac {1{\mbox{ unit))}{1{\mbox{ cl))))&&=&&75\times {\frac {12}{100)){\mbox{ units))&=9{\mbox{ units))\end{aligned))}$

Thus, a 750 ml bottle of wine at 12% ABV contains 75 cl × 12% = 9 units. Alternatively, the serving size in litres multiplied by the alcohol content as a number, the above example giving 0.75 × 12 = 9 units:

${\displaystyle {\begin{aligned}0.75{\mbox{ l))\times 12\%\times {\frac {100{\mbox{ units))}{1{\mbox{ l))))&&=&&0.75{\mbox{ l))\times {\frac {12}{100))\times {\frac {100{\mbox{ units))}{1{\mbox{ l))))&&=&&0.75\times 12{\mbox{ units))&=9{\mbox{ units))\end{aligned))}$

In the UK, both pieces of input data are usually mentioned in this form on the bottle, so are easy to retrieve.

When drink size is in fluid ounces (which differ between the UK and the US), the following conversions can be used:

One should bear in mind that a pint in the UK is 20 imperial fluid ounces, whereas a pint in the US is 16 US fluid ounces. However, as 1 imperial fl. oz. ≈ 0.961 US fl. oz., this means 1 imperial pint ≈ 1.201 US pints (i.e. 0.961 × 20/16) instead of 1.25 US pints.

Reference standard drinks

A standard drink is often different from a normal serving in the country in which it is served.^[33] For example, in the United States, a standard drink is defined as 0.6 US fluid ounce of ethanol per serving, which is about 14 grams of alcohol.^[27][34][32] This corresponds to a 12-US-fluid-ounce (350 mL) can of 5% beer, a 5-US-fluid-ounce (150 mL) glass of 12% ABV (alcohol by volume) wine, or a 1.5-US-fluid-ounce (44 mL) so-called "shot" of spirit,^[27] assuming that beer is 5% ABV, wine is 12% ABV, and spirits is 40% ABV (80 proof). Most wine today is higher than 12% ABV (the average ABV in Napa Valley in 1971 was 12.5% ^[35]), hence will be more than a standard drink. Similarly, although 40% ABV is standard for spirits, the amount of spirit in a mixed drink varies widely.

Beers

• Half an imperial pint (284 ml) of beer with 3.5% ABV contains almost exactly one UK unit; however, most beers are stronger. In pubs in the United Kingdom, beers generally range from 3.5 to 5.5% ABV, and continental lagers start at around 4% ABV. An imperial pint of such lager (e.g., 568 ml at 5.2%) contains almost 3 units of alcohol^[36] rather than the oft-quoted 2 units.
• Stronger beer (6–12%) may contain 2 units or more per half pint (imperial).
• A half-litre (500 ml) of standard lager or ale (5%) contains 2.5 units.
• One litre (1000 ml) of typical Oktoberfest beer (5.5–6%) contains 5.5–6 units of alcohol.
• A beer bottle is typically 333-355ml, approximately 1.7 units at 5%.
• 375 ml can of light beer (2.7% alcohol) = 0.8 Australian standard drinks
• 375 ml can of mid-strength beer (3.5% alcohol) = 1 Australian standard drink
• 375 ml can of full strength beer (4.8% alcohol) = 1.4 Australian standard drinks
• 355 ml can (12 fl oz) of 5% ABV beer = 1 US standard drink

Wines

• A "medium" glass (175 ml) of 12% ABV wine contains around 2.1 units of alcohol. However, British pubs and restaurants often supply larger quantities (large glass ≈ 250 ml), which contain 3 units. Red wines often have a higher alcohol content (on average 12.5%, sometimes up to 16%). Even though the sizes of wine glasses are defined in UK law, the terms large, medium, standard, etc. are not defined in law.
• Wine sold by the glass is often served in nearly full glasses. Wine served at home, or when bought by the bottle in, say, a restaurant, is usually served in glasses less than half filled; the capacity of a wine glass is not the only criterion for judging quantity.
• A 750 ml bottle of 12% ABV wine contains 9 units; 16% ABV wine contains 12 units; a fortified wine such as port at 20% ABV contains 15 units.
• 100 ml glass of wine (13.5% alcohol) = 1 Australian standard drink
• 150 ml glass of wine (13.5% alcohol) = 1.5 Australian standard drinks
• One 5 fl oz glass of 12% ABV table wine, or 148ml, is one US standard drink.

Fortified wines

• A small glass (50 ml) of sherry, fortified wine, or cream liqueur (≈20% ABV) contains about one unit.

Spirits

Most spirits sold in the United Kingdom have 35%-40% ABV. In England, a single pub measure (25 ml) of a spirit contains one unit. However, a larger 35 ml measure is increasingly used (and in particular is standard in Northern Ireland^[37]), which contains 1.4 units of alcohol at 40% ABV. Sellers of spirits by the glass must state the capacity of their standard measure in ml.

In Australia, a 30 ml shot of spirits (40% ABV) is 0.95 standard drinks.

In the US, one shot of 80 proof liquor is 1.5 fl oz or 44ml, and one US standard drink.

Mixed spirits and alcopops

• 440 ml can of pre-mix spirits (approx. 5% alcohol) = 1.7 Australian standard drinks
• 440 ml can pre-mix spirits (approx. 7% alcohol) = 2.4 Australian standard drinks
• According to Alcohol and You Northern Ireland resource website, "Most alcopops contain 1.1–1.5 units per bottle. For example, a normal 275 ml bottle of WKD contains 1.1 units, whereas Bacardi Breezer and Smirnoff Ice both contain 1.5 units of alcohol."^[38]

Recommended maximum

From 1992 to 1995, the UK government advised that men should drink no more than 21 units per week, and women no more than 14.^[39] (The difference between the sexes was due to the typically lower weight and water-to-body-mass ratio of women).^[40] The Times claimed in October 2007 that these limits had been "plucked out of the air" and had no scientific basis.^[41]

This was changed after a government study showed that many people were in effect "saving up" their units and using them at the end of the week,^[42][43] a form of binge drinking. Since 1995 the advice was that regular consumption of 3–4 units a day for men, or 2–3 units a day for women, would not pose significant health risks, but that consistently drinking four or more units a day (men), or three or more units a day (women), is not advisable.^[44]

An international study^[45] of about 6,000 men and 11,000 women for a total of 75,000 person-years found that people who reported that they drank more than a threshold value of 2 units of alcohol a day had a higher risk of fractures than non-drinkers. For example, those who drank over 3 units a day had nearly twice the risk of a hip fracture.

Relation to blood alcohol content

As a rough guide, it takes about one hour for the body to metabolise (break down) one UK unit of alcohol, 10 ml (8 grams). However, this will vary with body weight, sex, age, personal metabolic rate, recent food intake, the type and strength of the alcohol, and medications taken. Alcohol may be metabolised more slowly if liver function is impaired.^[24] For other countries, it may be easiest to convert to UK units. For example, in the United States one standard drink contains 14 grams ≈ 1.75 units of alcohol, and so a US standard drink takes the body about an hour and three-quarters to process. Blood alcohol content can more accurately be estimated by using Widmark's formula.^[46]

Labeling

Australia introduced standard drink labelling in the 1990's,^[47] and New Zealand followed with a labelling requirement starting in 2002.^[48] The labels were criticized for being too small to read. A focus group study found that most student drinkers used the labels to choose stronger drinks and identify the cheapest method of getting drunk, rather than to drink safely.^[47]

In the UK in March 2011, alcohol companies voluntarily pledged to the UK Department of Health to implement a health labelling scheme to provide more information about responsible drinking on alcohol labels and containers. The pledge stated:^[49]

"We will ensure that over 80% of products on shelf (by December 2013) will have labels with clear unit content, NHS guidelines and a warning about drinking when pregnant."

At the end of 2014, 101 companies had committed to the pledge labelling scheme.^[49]

There are five elements included within the overall labelling scheme, the first three being mandatory, and the last two optional:

1. Unit alcohol content per container (mandatory), and per serving (optional). Typical servings deliver 1–3 units of alcohol.^[50]
2. Chief Medical Officer's daily guidelines for lower-risk consumption
3. Pregnancy warning (in text or as a graphic)
4. Mention of "drinkaware.co.uk" (optional)
5. Responsibility statement (e.g., "please drink responsibly") (optional)

Further detailed specifications about the labelling scheme are available from the "Alcohol labelling tool kit".^[51]

Drinks companies had pledged to display the three mandatory items on 80% of drinks containers on shelves in the UK off-trade by the end of December 2013.^[51] A report published in November 2014, confirmed that UK drinks producers had delivered on that pledge with a 79.3% compliance with the pledge elements as measured by products on shelf. Compared with labels from 2008 on a like-for-like basis, information on Unit alcohol content had increased by 46%; 91% of products displayed alcohol and pregnancy warnings (18% in 2008); and 75% showed the Chief Medical Officers' lower risk daily guidelines (6% in 2008).^[52]

Studies published in 2021 in the UK showed that the label could be further enhanced by including pictures of units and a statement of the drinking guidelines - this would help people understand the recommended limits better.^[53][54]