Inverter Size Calculator

List what runs at once, allow for motor start-up surge, and find the inverter size and battery current you need.

This sizes an inverter for running watts and motor start-up surge. The example rows are a small workshop, so edit or remove them. Everything is worked out in your browser. Nothing is saved or sent anywhere.

1. Tools and appliances

Enter the running watts from the label. Start-up × is how many times the running watts the item draws for a moment as its motor starts: about 1 for lights, chargers and radios, about 2 for drills, jigsaws, angle grinders and sanders, and about 3 for compressors, bench grinders, table saws, drop saws, pumps and fridges. Check the maker's figure if you have it. Tick On together for everything that could be running at the same moment.

2. Assumptions

So the inverter isn't running at its limit (0 to 100%).
Nominal system voltage.
Used for the battery current (50 to 100%).

3. Results

How it was worked out

    Before you rely on it

    • The surge figure assumes one motor starts at a time, on top of everything else already running. If two motors could start together, add both.
    • Inverter surge ratings are only for a short time, and makers measure them differently. Check that the inverter's surge rating and how long it lasts covers your hardest-starting tool. If an inverter trips every time a tool starts, its surge rating is too low.
    • A pure sine inverter is the right choice for a workshop. See Pure Sine vs Modified Sine Inverters.
    • The battery, its BMS, the fuse and the cables must all handle the battery current shown, and the surge current too.
    • This is a planning estimate only, not a system design, wiring specification or safety assessment. Real results depend on your location, weather, shading and the gear you choose. Check the manuals and specifications for your panels, battery, inverter and charge controller.
    • Safety: in Australia, any work on 240V AC wiring, including connecting an inverter, battery or solar system to a home's switchboard or fixed wiring, must be done by a licensed electrician. Grid-connected systems also need approval from your electricity network.

    Next steps

    Read more in Running Power Tools Off Solar: Inverter Size and Surge. High battery current? Check the 12V / 24V / 48V Picker.

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