The strength of an alcoholic drink is measured by the percentage
of alcohol by volume (abv) and is seen as the % written on the product.
The term "units" is now used to make it easier for people to understand
how much they are drinking. Many products now have the number of units
contained in each measure written on them as well as the legally required
%.
As a rough guide to what you're drinking:
While many drink manufactures now print the number of units on their
products, many still do not. This can make it difficult to understand
how much you are drinking, especially if the product is higher than
usual in %, or what is often called export strength. If a product
does not have the units marked on them, you can still calculate this
for yourself using the following calculation:
Take amount in the total bottle, can, or size of drink and multiply
this by the % written on the product (ABV) and divide by 1,000. This
will give you the total number of units in the measure you are drinking.