The alcohol content of alcoholic beverages varies from one beverage to the other. By legislation the alcohol (ethanol) content by volume (% abv) has to be indicated on the label of alcoholic beverages.
To calculate the number of drinking units, it is necessary to know the grams of alcohol contained in the alcoholic beverage and how to translate % abv into grams of alcohol.
To translate volume (e.g. ml) to mass (e.g. g) and vice versa, it is necessary to know the density. Alcohol density d=0.8g/ml.
Thus: a wine at 12.5 % vol contains 12.5ml of alcohol/100ml of wine x 0.8 g/ml = 10g of alcohol/100 ml of wine.
This is the equivalent of 1 drinking unit (= 10 g).
(A drinking unit can vary from 8-14g of alcohol depending on the country)
This way it is easy to assess the number of units you are consuming.
For example, 125 ml of wine (12.5% vol), will translate into 1.25 drinking units and 175ml of wine (12.5% vol), will translate into 1.75 drinking units.
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