How much is 4 units of alcohol?

a unit normally stands for 1 glass of an alcoholic consumption. This mean, most basically, 1 glass of beer (5% alcohol).

Standard glasses of wine, shot, beer etc. are based on the unit system. This means that a standard glass of wine, and standard glass of beer and a standard shot glass contain more or less the same amount of alcohol (of course some spirits and wines/beers are stronger than the other).

Most basic, a unit of alcohol means 1 liter with 1% alcohol in it.

Thus 4 units equals four liters with 1% alcohol, which then again equals 4 glasses (250 mL) of 5% beer.

Hope that helps