Size the inverter around simultaneous power, then check surges
Daily kWh tells you how much energy a home uses. Inverter kW is driven by how much power may be demanded at the same time. Add the appliances that can run simultaneously, then allow sensible design headroom.
Inverter size calculator
Use manufacturer surge curves and real appliance data before choosing an inverter, especially for pumps, compressors and air conditioners.
Motor loads need a separate surge check
Pumps, compressors and some air conditioners can draw substantially more power during start-up than during steady operation. A simple continuous-load calculator cannot determine whether a particular inverter will start a specific motor. Check manufacturer surge curves, motor starting method and installer design.
Do not forget phase and backup-output limits
Three-phase properties, dedicated EPS/backup outputs and per-phase limits can make the practical rating more complicated than one headline kW number.