Inverter Sizing Calculator

About this calculator

An inverter has to handle two different demands from the loads it powers: the continuous (running) wattage it must sustain indefinitely, and a much higher surge wattage that motor-driven loads — refrigerator compressors, power tools, well pumps — draw for a fraction of a second at startup, often 2-3× their running wattage. Sizing an inverter only for running watts risks it tripping or shutting down the moment a compressor kicks on; the inverter's own conversion efficiency (typically 85-95%) also means the DC input power it draws from a battery is always somewhat higher than the AC power it delivers.

This calculator takes your total running load, a surge factor for motor-driven equipment, and the inverter's efficiency, then recommends a continuous wattage rating, the expected peak surge demand, and the DC input power required. RV and van-life owners sizing a power system, off-grid solar installers, and homeowners planning backup power for outages use it to pick an inverter that won't nuisance-trip under real-world startup surges while avoiding paying for far more capacity than the loads actually need.