An inverter supplies an AC load from a DC battery. Enter the load’s real watts, single-phase AC voltage and power factor, then the measured battery voltage, inverter efficiency and any separate idle draw.

Formula: AC current = real load W ÷ (AC V × load power factor); battery input W = AC load W ÷ (efficiency % ÷ 100) + separate idle W; battery A = battery input W ÷ battery V

Worked example

A 600 W single-phase load at 120 V and PF 1 draws 5 AC A. With 90% inverter efficiency plus 10 W separate idle draw, the battery supplies about 676.67 W, or 52.86 A at 12.8 V under load.

Two sides of the inverter use different volts

The AC current uses the load’s power factor and AC voltage. The battery current uses DC input watts and battery voltage at the operating point. DOE describes an inverter as the device converting DC to AC; the two current values should not be equated.

Efficiency and idle draw are separate inputs

Enter an efficiency appropriate to the expected load. Idle draw is added only if it is not already included in the efficiency data. A value of 0 W is allowed. The displayed loss excludes that separate idle amount.

A steady-load estimate

Motor startup, surge rating, waveform, cable loss, battery sag, temperature and multiple AC phases are outside this model. It does not size wiring, fuses or an inverter for a particular installation.

Explore the related calculation

For a different starting point, try the battery runtime calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

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