The definition of 'a unit of alcohol' differs depending on which country is being talked about. For example:
One unit of alcohol is defined as containing 10ml or 8g of pure alcohol; the amount of alcohol the average adult can process within an hour. This equates to:
- 1 unit per percentage point abv in one litre of drink
- Approximately a half (imperial) pint (284ml) of 3.5% abv drink (0.994 units)
- 83.¯3ml of 12% abv wine (175ml=2.1 units, 250ml=3 units)
- 25ml measure of 40% abv spirit
A standard drink is defined as containing 0.6 fluid ounce (17.05ml) or 14.0g of pure alcohol. This equates to
- 12-ounces of 5% abv beer.
- 8-ounces of 7.5% abv malt
- 5-ounces of 12% abv wine.
- 1.5-ounces (44.3ml) or a “shot” of 40% abv distilled spirits or liquor.
A standard drink is defined as containing 12.5ml or 10g of pure alcohol. This equates to
- 375 ml bottle or can of 3.¯3% abv lager/beer.
- 104 ml of 12% abv wine (100ml~=1 unit, 1.50ml ~= 1.44 units)
- ~30ml measure of 40% abv spirit (0.96 units)
A standard drink is defined as containing 16.875ml or 13.6g of pure alcohol. This equates to
- 341ml/12oz of 5% abv lager/beer.
- 5 oz 12% abv wine
- ~40ml measure of 40% abv spirit (1.06 units)
Based on data from Sensible Drinking the amount of alcohol is stated in the table in both grams and millilitres. The number of standard drinks contained in 500ml of beer of 5% ABV (a typical large drink of beer) is stated for comparison, along with daily and weekly limits, where data is available. Blank cells indicate either no guidelines given, or no data available.
|Country||g/Std Drink||ml (based on 12.67g/ml)||500ml@5%||g/day Male||g/day Female||g/week Male||g/week Female|
|Malta||3 drinks||2 drinks|
|WHO||3 drinks on average||2 drinks on average|
Controversially, however, Richard Smith, former editor of the British Medical Journal and a member of the Royal College of Physicians, which came up with the UK report from a committee of doctors in 1987, which set out weekly limits of 21 units(168g) for men, and 14(98) units for women, has admitted that the weekly limits were essentially "plucked out of thin air.":
[Richard Smith] recalled that the committee could find "no decent data" on the subject, but felt obliged to make a recommendation nonetheless.
- He said: "They weren't really based on any firm evidence at all. It was a sort of intelligent guess by a committee." 
And from Richard's own blog
Kristin Wolfe, head of alcohol policy at SAB Miller, one of the world’s largest brewers, said that 80-90% of people are responsible drinkers and that the harm results from the other 10-20%. She accepted that people should be given information on safe limits, but she pointed out that there is considerable variation in advice around the world: in Australia the advised limit is 20 grams a day, whereas in Portugal its 37 grams; in the US a unit is 14 grams, contrasting with the 8 grams in Britain.
Subsequent studies had shown that the guidelines should have been higher but were ignored by successive governments.
More recently, Oxford University have produced a report recommending that the daily limit be reduced to 1/2 a (UK) unit a day (about 1/2 pint beer):
An Oxford University study found that the beneficial effects of alcohol have been exaggerated and thousands of deaths from cancer and liver cirrhosis could be prevented.
This level may “not be compatible with optimum protection of public health', the research published in the journal BMJ Open found.
"[...] A couple of pints or a couple of glasses of wine per day is not a healthy option.
"We are not telling people what to do[...]
- ↑ http://www.drinkaware.co.uk/alcohol-and-you/health/guide-to-alcohol-units-and-measures
- ↑ http://www.cdc.gov/alcohol/faqs.htm#standDrink
- ↑ http://www.health.gov.au/internet/alcohol/publishing.nsf/Content/standard
- ↑ http://www.agingincanada.ca/a_standard_drink.htm
- ↑ http://www.nhmrc.gov.au/_files_nhmrc/publications/attachments/ds10-alcoholqa.pdf
- ↑ http://www.ara.co.za/alcohol-facts
- ↑ Safe drinking limits to be reviewed - The Telegraph
- ↑ Richard Smith: Battling over safe alcohol limits - The BMJ
- ↑ Safe drinking limits 'were simply a guess' - Daily Mail Online
- ↑ Sticking to a quarter pint of beer a day would save thousands of lives: research - The Telegraph