[[Image:Red Wine Glas.jpg|thumb|right|A large glass of red wine contains about three units of alcohol]]
In Britain a '''unit of alcohol''' is defined as 10 [[litre|millilitres]] (or approximately 8 [[gram]]s) of [[ethanol]] (ethyl alcohol). It is used as a basis for guidelines on consumption of [[alcoholic beverages]]; the number of units contained in a typical drink is publicised and marked on bottles.

== Formula ==
The number of units of alcohol in a drink can be determined by multiplying the volume of the drink (in millilitres) by its percentage [[Alcohol by volume|ABV]], and dividing by 1000 (or litres × % abv).

Thus a [[pint]] (568ml) of beer at 4% ABV contains

<math>\frac{568 \times 4}{1000} = 2.3\mbox{ units}</math>

In the [[metric system]] there is 1 unit per percentage point of ABV in 1 litre of a drink; e.g., 37.5 units in a litre of a typical whisky with 37.5 ABV.

== Quantities ==
It is often misleadingly stated that a unit is supplied by a small glass of wine, half a pint of beer, or a single measure of spirits.<ref>{{cite web
| last =
| first =
| authorlink =
| coauthors =
| title = Alcohol and the athlete
| work =
| publisher = BUPA
| date =
| url = http://www.bupa.co.uk/health_information/html/healthy_living/lifestyle/exercise/diet_exercise/athalc.html
| format =
| doi =
| accessdate = 2007-07-29 }}</ref> Such statements are misleading because they do not reflect the large differences in strengths and measures of wines, beers and spirits.<ref>{{cite web
| last =
| first =
| authorlink =
| coauthors =
| title = Alcohol
| work =
| publisher =
| date =
| url = http://www.nutrition.org.uk/home.asp?siteId=43&sectionId=610&parentSection=324&which=undefined
| format =
| doi =
| accessdate = 2007-07-21 }}</ref>
<ref>{{cite web
| last =
| first =
| authorlink =
| coauthors =
| title = Alcohol
| work =
| publisher = BBC - Health
| date =
| url = http://www.bbc.co.uk/health/healthy_living/nutrition/drinks_alcohol.shtml
| format =
| doi =
| accessdate = 2007-07-29 }}</ref>

* Beers
**A half pint (284ml) of ordinary strength (3.5-4% ABV) [[beer]] contains about one unit. However, some beers (especially lager) are stronger. In pubs, beers generally range from 4% to 5.5% ABV with continental lagers starting at around 5% ABV. A pint of such lager (568ml at 5.2% for example) is almost 3 units of alcohol, rather than the often-quoted value of 2 units per pint.
**A 500ml can/bottle of standard [[lager]] (5%) generally contains around 2.5 units.
**'Super-strength' or strong [[pale lager]] may contain as much as two units per half pint.

*Wines
**A small glass (125[[millilitre|ml]]) of 8% [[Alcohol by volume|abv]] [[wine]] contains one unit, or 8&nbsp;g (0.25&nbsp;oz) of alcohol. However, British pubs and restaurants usually supply larger quantities (medium: 175 ml or large: 250 ml), and few wines are as weak as 8%; 12% is more usual. A typical pub measure (medium glass - 175 ml) of white wine (at 12%) contains around 2 units (actually 2.1) and a large glass (250 ml) contains 3.0 units. Red wine, which usually has a higher alcohol content (up to 16%), contains for an average 14% abv. an alcohol content of 3.5 units for a large (250 ml glass), approximately one-sixth higher than a typical white wine. Just two bottles of 14% abv. red wine a week will supply the maximum intake of alcohol for a man recommended by UK health guidelines.
**A 750ml standard bottle of 12% wine contains 9 units. Many wines (especially New World red wines) may contain 14% ABV or more, which is 10.5 units of alcohol per bottle.

*Fortified wines, etc.
**A small glass (50ml) of [[sherry]], fortified wine, or cream liqueur (approx. 20% abv) contains about one unit.

*[[Distilled beverage|spirits]]
**Most spirits sold in the UK have 40% ABV or slightly less. A single pub measure (about 25ml) of such a spirit contains one unit. However, a larger single measure of 35 ml is now often sold, resulting in the consumption of 1.4 units of alcohol.

== Limits ==
Since 1995 the UK government has advised that regular consumption of between three and four units a day for men and between two and three 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.{{Fact|date=October 2007}} Previously (from 1992 till 1995) the advice was that men should drink no more than 21 units per week, and women no more than 14.{{Fact|date=October 2007}} This was changed because a government study showed that many people were in effect "saving" up their units and "using" them at the end of the week, {{Fact|date=October 2007}}a phenomenon referred to as [[binge drinking]]. The difference between sexes is given due to the (typically) lower weight and water-to-body-mass-ratio of women.

It was claimed in October 2007 that these limits had been "plucked out of the air" and have no scientific basis.<ref>[http://timesonline.co.uk/tol/life_and_style/food_and_drink/article2697975.ece Drink limits ‘useless’], The Times, October 20, 2007</ref>

An international study (Kanis, 2005) of almost 6,000 men and 11,000 women found that persons who reported that they drank more than 2 units of alcohol a day had an increased risk of fractures compared to non-drinkers. For example, those who drank over 3 units a day had nearly twice the risk of a hip fracture.<ref>http://www.ncbi.nlm.nih.gov/sites/entrez?md=retrieve&db=pubmed&list_uids=15455194&dopt=AbstractPlus</ref>

==See also==
*[[Standard drink]]

==References==
{{reflist}}

[[Category:Units of measure]]
[[Category:Alcoholic beverages]]