How much power does an inverter draw?

How much current is drawn from a 12V or 24V battery when running a battery inverter?

Documented in this article are common questions relating to the inverter draw (inverter amp draw or inverter current draw) for 12v (or 24v) batteries. If you’re looking for information relating to your 2000 watt inverter amp draw, we’ve got a breakdown of expectant voltage and efficiencies for a range of wattages below.

How much current is drawn from the 12V (or 24V) battery when running a battery inverter?

The simple answer is: divide the load watts by 10 (20). E.g. For a load of 300 Watts, the current drawn from the battery would be:


Watts to amps 12v calculator

300 ÷ 10 = 30 Amps

Watts to amps 24v calculator

(300 ÷ 20 = 15 Amps)


Notes on wattage rating vs load:

  • It is the actual load watts, not the inverter rating or (inverter size) that counts. So a 1500 watt inverter with a 500 watt load would be 50 (25) Amps, not 150 (75) Amps. The same inverter with a 1200 Watt load would draw 120 (60) Amps, which would be the same amount as a 1200 Watt inverter at load capacity. And for a 2000w 12v pure sine wave inverter? We think you get the picture. The 2000 watt inverter amp draw depends on its watt load.
  • For a quick idea of how long a battery will last without the alternator running, think of the load watts in terms of headlight watts.


How long will my battery last with an inverter load of 1000 Watts?

About as long as having 10 x 100W driving lights on. You know a normal car battery won't last long even with just 2 x 55W headlights and 4 x 5W park/tail lights - 130W total.

For a more accurate calculation of battery current: Divide load watts by actual battery voltage, this will be in the range 12-14V (24-28V).

Then to allow for inverter efficiency, typically 85%, divide the figure by 0.85. So your inverter calculator is thus:

For a 300W load at 12 volts....300 ÷ 12 ÷ 0.85 = 29.4 Amps.

For a 300W load at 14 volts....300 ÷ 14 ÷ 0.85 = 25.2 Amps.

You can see the simple divide by 10 gives an easy "worst case" guide for your power requirements.



For a 300W load at 24V....300 ÷ 24 ÷ 0.85 = 14.7 Amps.

For a 300W load at 28V....300 ÷ 28 ÷ 0.85 = 12.6 Amps.

You can see the simple divide by 20 gives an easy "worst case" guide.


Note: Figures in brackets are for 24V systems.