12V Install Tools & Testers

Charger & Inverter Sizing Calculator

Size an inverter for your AC appliances, then work out the charger current needed to refill your battery in time.

This gives an inverter-size and charger-current estimate only, not a complete system design. Part 1 sizes an inverter for your 240V AC appliances. Part 2 works out the charging current needed to refill your battery in the time you have. The example rows are only a starting point, so edit or remove them. Everything is worked out in your browser. Nothing is saved or sent anywhere.

1. Inverter: your AC appliances

Enter each 240V appliance you'll run through the inverter: its running watts (check the label or manual) and how many. Choose a load type to estimate the start-up surge (Resistive: kettles, heaters, lights; Electronics: laptops, TVs, chargers; Motor / compressor: fridges, pumps, power tools, about 3 times running watts), or enter the surge watts from the manual if you know them. Untick Same time for items you won't run together with the others.

2. Inverter assumptions

These defaults are common starting points, not rules. Change any of them to suit your gear.

The battery voltage the inverter runs from.
Typical starting value (80 to 98%).
Headroom so the inverter isn't run flat out (10 to 50%).
From your battery's specifications. Leave blank to skip this check.

3. Inverter results

How it was worked out

    4. Charger: refill your battery

    Work out the charging current needed to put back what you use in the time you have, for a DC-DC charger while driving or a plug-in mains charger.

    Sets the charge efficiency and suggested maximum charge rate.
    Rated capacity (10 to 2,000 Ah).
    Of the rated capacity (1 to 100%). Our Battery Size Calculator can estimate your daily use.
    For example, hours of driving (0.25 to 24).
    From your battery's specifications. Leave blank to use a typical limit.

    5. Charger results

    How it was worked out

      Before you buy an inverter or charger

      • This calculator provides an estimate only. It is not a guaranteed specification, and it is not a complete system design, wiring specification or safety assessment. Check the manuals for your battery, inverter, charger and appliances.
      • Start-up surge figures vary a lot between appliances. Motors and compressors can draw several times their running watts for a moment. Use the maker's surge figure where you have it.
      • The surge result assumes only one appliance starts at a time while the others are already running.
      • Size the fuse and cable for the inverter's full rated DC current, not just your load. Fit the fuse or circuit breaker close to the battery. See our 12V Cable and Fuse Size Guide.
      • Any work on 240V AC wiring, including hard-wiring an inverter into a vehicle or caravan circuit, must be done by a licensed electrician.

      Next steps

      Compare charger sizes in What Size DC-DC Charger Do I Need?, and check your daily balance with the Solar & Charging Check.

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