Inverter Size Calculator
Calculate the recommended inverter size for off-grid or backup power, accounting for continuous load, motor surge, and safety margins.
Results
What is it?
An inverter converts DC battery power to AC power for home appliances. Two ratings matter: continuous watt rating (constant load) and peak/surge watt rating (for motor start-up). Inductive loads like refrigerators, pumps, and air conditioners draw 3-7x their running wattage at startup — the inverter must handle this surge without shutting down.
How to use
1. Add up the running wattage of all appliances you plan to run simultaneously. 2. Identify the single largest motor in your system (refrigerator, pump, HVAC) and multiply its running watts by 5-7 for the surge estimate. 3. Enter your desired safety buffer percentage. 4. The recommended inverter size is rounded up to the nearest standard 500W increment.
Example scenario
Running: refrigerator (150W), lights (100W), laptop (60W), fans (150W) = 460W continuous. Refrigerator surge = 150 x 5 = 750W. Recommended continuous with 25% buffer = 460 x 1.25 = 575W rounded to 1,000W. Peak needed = 460 + 750 = 1,210W rounded to 1,500W. Buy a 1,500W inverter with 3,000W surge rating.
Pro tip
Always check both the continuous AND surge rating of an inverter. A cheap 2,000W inverter may only handle 2,000W surge for 2 seconds — insufficient for a compressor. Quality inverters list separate continuous and surge ratings. Size your inverter at 120-150% of your continuous load to improve efficiency — inverters are most efficient at 50-75% of their rated capacity.