About 1 to 1.5 kW units per room. Your unit air conditioning supplier can give you a very quick rule of thumb design.
If you are using a central packaged unit, you add up the requirement for individual rooms. It is usual to estimate on a per sq.m basis. The same goes for split units.
If you need anything better, then a more detailed heat loss calculation, using Carrier tables, or ASHREA Handbook is warranted.