Unit of alcohol

In Britain a unit of alcohol is defined as 10 millilitres (or approximately 8 grams) 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 ABV, and dividing by 1000 (or litres × % abv). Thus, one pint (568ml) of beer at 4% ABV contains:

The formula uses the quantity in millilitres divided by 1000; this has the result of there being exactly one unit per percentage point per litre of any alcoholic beverage.

As the volume of alcoholic drinks is becoming increasingly shown in centilitres, discerning the number of units in a drink can be as simple as multiplying volume by percentage (converted into a fraction of 1). Thus, 75 centilitres of wine at 13 % ABV contains:

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. Such statements are misleading because they do not reflect the large differences in strengths and measures of wines, beers and spirits.

Beers

• A half pint (284ml) of ordinary strength (3.5-4% abv) beer contains about one unit. However, some beers 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%) contains 2.5 units.
• 'Super-strength' or strong pale lager may contain as much as two units per half pint.
• One litre of typical Oktoberfest beer (5.5% to 6%) contains 5.5 to 6 units of alcohol.

Wines

• A small glass (125ml) of 8% abv wine contains one unit 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 typical. A standard pub measure (medium glass - 175 ml) of white wine (at 12%) contains around 2 units and a large glass (250 ml) contains 3 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 bottle of 12% wine contains 9 units. Many wines may contain 14% abv or more, which is just over 10 units of alcohol per bottle.

Fortified wines

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

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.
  

Alcopops

• Most alcopops contain 1.4 to 1.5 units per bottle. For example, a regular 275ml bottle of WKD contains 1.4 units, whereas Bacardi Breezer and Smirnoff Ice both contain 1.5 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. Previously (from 1992 until 1995) the advice was that men should drink no more than 21 units per week, and women no more than 14. 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,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.

An international study 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.