The alcohol content in wine is measured in alcohol-by-volume (ABV) which is a standard measure based on the percentage in a given volume.
Units are a simple way to express the amount of alcohol in a drink which makes it easier to compare different types of alcohol.
This is useful information because a small measure of a high alcohol content drink could easily have more alcohol in it than a large measure of a lower alcohol drink.
You can work out the units with this handy sum:
Strength (ABV) x Volume (ml) / 1000 = Number of units
So, as an example, a bottle of alcohol-free wine at around 0.2% ABV:
0.2% ABV x 750ml divided by 1000 = 0.15 units (ie, 15% of one unit).
By comparison, a bottle of 13% ABV alcoholic wine is 9.8 units.
Men and women are advised to consume no more than 14 units of alcohol spread over a week. Consuming all 14 units in one session is binge drinking and is harmful. Anyone who drinks alcohol is advised to have two or three alcohol-free days in a week.