Inverter Size Calculator

Add the running wattage of all AC appliances you want to run simultaneously. Multiply by 1.25 as a safety factor to allow for surges and inefficiency. Select an inverter rated at or above this total. Also check the inverter's surge capacity against the startup wattage of your largest motor (usually 3-5x running watts for compressor motors).

Continuous wattage is the rated output an inverter can sustain indefinitely. Surge wattage (peak power) is the short burst capacity for starting motors and compressors, typically 2-3 times the continuous rating. Inverters must meet both the continuous load and the startup surge of the largest motor.

Inverter efficiency is the percentage of DC battery power converted to AC output. Modern sine wave inverters are typically 90-95% efficient at full load, dropping to 85-90% at light loads. A 1,000W load at 90% efficiency draws 1,111W from the battery (1,000 / 0.90). Higher efficiency reduces battery drain and heat generation.

Pure sine wave inverters produce AC identical to grid power and work with all appliances including sensitive electronics, variable-speed motors, and audio equipment. Modified sine wave inverters are less expensive but may cause problems with some motors, medical equipment, and electronics. For most modern appliances, pure sine wave is recommended.

Runtime = (Battery capacity in Ah x Battery voltage x Inverter efficiency) / Load in watts. For a 200 Ah, 24V battery bank at 90% efficiency running a 500W load: (200 x 24 x 0.90) / 500 = 8.64 hours. Actual runtime will be less at deep discharge, high temperature, or when battery is partially depleted.