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Inverter Size Calculator

Continuous + surge watts to the right inverter

Quick answer

Continuous rating = simultaneous running watts + ~20%; surge rating must cover the biggest motor start (2–3× running). Always pure sine wave, and size the DC cable to the current the inverter pulls, not the load watts.

600W
600W
System voltage

Continuous rating

1000W

Minimum surge rating

2000W

DC draw at full load

~91.7A

Size inverter cable & fuse to this

Shop 1000W pure sine inverters
  • Use a pure sine wave inverter — modified sine damages motors, chargers and some electronics.
  • At full load this inverter pulls ~91.7A from a 12V bank — size the inverter cable and fuse to that, not the running watts.

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Frequently asked questions

What size inverter do I need?

Add up the watts of everything you will run at the same time, add ~20% headroom for the continuous rating, and make sure the surge rating covers the biggest motor start (fridges, pumps and power tools can surge 2–3× their running watts).

Pure sine or modified sine?

Pure sine wave. Modified sine can damage motors, chargers, CPAP machines and some electronics, and runs others hot or noisily. The small saving is not worth it.

Why does the inverter pull so much from my battery?

A 1000W load at 12V draws over 90A from the battery once you allow for conversion losses. That is why inverter cable and fuses must be sized to the DC current, and why big inverters need a lithium bank.

Can I run a kettle or microwave?

Only with a large inverter (1500W+) and a big lithium battery with heavy cable. A 2kW kettle can flatten a 200Ah lithium bank in under an hour, so many vanlifers use gas for boiling instead.