Unit of alcohol

A "large" (250 ml) glass of 12% ABV red wine has about three units of alcohol. A "medium" (175 ml) glass, such as the one shown, has about two units.[Note 1]

Units of alcohol are a measure of the volume of pure alcohol in an alcoholic beverage. They are used in some countries as a guideline for alcohol consumption. In some other countries a "standard drink", different from country to country, is defined for the same purpose.

One unit of alcohol is defined as 10 millilitres (7.9 grams) in the United Kingdom;[1] typical drinks provide 1–3 units.[2] In Australia "a 'standard drink' is the amount of a beverage that contains ten grams of alcohol at 20 degrees Celsius (12.7 ml)".[3] In the US a "standard" drink is one that contains about 0.6 US fluid ounces[4] or 14 grams of alcohol, about 77% more than a UK unit.[5]

Labelling is usually required to give an indication of alcoholic content of a serving. In the United Kingdom the number of units in a typical serving is printed; Australia requires that "the label on a package of an alcoholic beverage must include a statement of the number of standard drinks in the package".[3]

A typical healthy adult can metabolise about one unit per hour, depending on many factors.

Formulae

The number of 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% ABV contains:

$\frac{568\mbox{ ml} \times 4}{1000} {{=}} 2.3\mbox{ units}$

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

Since 4% can be expressed as .04, .04 × 568 ml gives the amount of alcohol in terms of ml—which, when divided by 10, shows the number of units.

When the volume of an alcoholic drink is shown in centilitres, determining the number of units in a drink is as simple as volume × percentage (converted into a fraction of 1).

Thus, 750 millilitres of wine (the contents of a standard wine bottle) at 12% ABV contain:

$750 \times 12/1000 {{=}} 9.0\mbox{ units}$

Quantities

It is often stated that a unit of alcohol is supplied by a small glass of wine, half a pint of beer, or a single measure of spirits.[6] Such statements may be misleading because they do not reflect differences in strength of the various kinds of wines, beers, and spirits.

Chart showing alcohol unit count for drink size and ABV

The advent of smartphones led to the creation of apps which inform consumers of the number of units contained in an alcoholic drink.[7]

Beers

• A half pint (284 ml) of beer with 3.5% ABV contains almost exactly one unit; however, most beers are stronger. In pubs in the United Kingdom, beers generally range from 3.5%–5.5% ABV, and continental lagers start at around 5% ABV. A pint of such lager (e.g., 568 ml at 5.2%) contains almost 3 units of alcohol[8] rather than the oft-quoted 2 units.
• Stronger beer (6%–12%) may contain 2 units or more per half pint.
• 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.

Wines

• A medium glass (175 ml) of 12% ABV wine contains around two 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%).
• 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.

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 40% ABV or slightly less. In England a single pub measure (25 ml) of a spirit contains one unit. However, a larger 35ml measure is increasingly used (and in particular is standard in Northern Ireland[citation needed]), 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.

Time to metabolise

On average, it takes about one hour for the body to metabolise (break down) one unit of alcohol. However, this can 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.[2]

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.[10] (The difference between the sexes was due to the typically lower weight and water-to-body-mass ratio of women[citation needed].) The Times reported in October 2007 that these limits had been "plucked out of the air" and had no scientific basis.[11][12]

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, a phenomenon referred to as binge drinking.[citation needed] 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.[13]

An international study[14] 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.

Notes

1. ^ Even though the sizes of wine glasses are defined in UK law, the terms "large", "medium", "standard" etc are not defined in law.

References

1. ^
2. ^ a b UK NHS:How long does alcohol stay in your blood?, reviewed 2013
3. ^ a b Guide to Labelling of Alcoholic Beverages
4. ^ The US fluid ounce is about 4% larger than the no-longer-used Imperial fl.oz.
5. ^ rethinkingdrinking.niaaa.nih.gov, US NIH Web site:What's a "standard" drink?
6. ^ "Alcohol and the athlete". BUPA. Archived from the original on 7 June 2007. Retrieved 29 July 2007.
7. ^
8. ^ The volume of the drink in litres multiplied by its percentage strength in ABV give the number of units. In this case, 0.568 × 5.2 gives 2.95, i.e., almost 3 units.
9. ^ "Question:- "How much alcohol is there in WKD vodka blue?"". Retrieved 27 April 2013.
10. ^ "Health Effects of Alcohol". Drinkaware.co.uk. Retrieved 27 May 2013.
11. ^ Drink limits ‘useless’, The Times, 20 October 2007
12. ^ The great alcohol myth, The Guardian, 26 January 2009
13. ^ "Sensible drinking". NIdirect Government Services. 2013. Retrieved 27 May 2013.
14. ^ Kanis JA, Johansson H, Johnell O et al. (July 2005). "Alcohol intake as a risk factor for fracture". Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA 16 (7): 737–42. doi:10.1007/s00198-004-1734-y. PMID 15455194.