Working out units is dead easy. 1 litre of 100% alcohol is 100 units. Litre of whisky at 40% is therefore 40 units. Litre of wine at 12% is 12 units. Litre of beer at 4% is 4 units. The only issue then is working out what 70 or 75 cl is and you need to know that 1 UK pint is 568ml and 1 US pint is 473ml. Easier to just say a bottle of wine is 3/4 of a litre. Bottle of whisky is just under. UK pint is just over 1/2 a litre while a US pint is just under.

Seemples :-)