Inverter specs mix watts, amps and volts, and it is easy to get confused. This simple calculator converts between them and shows how much current an inverter really pulls from the battery.
Use the first box to solve for watts, amps or volts, and the second to see the DC current at 12V, 24V and 48V for any load.
Watts, amps and volts calculator
Fill in any two boxes and leave the third one empty.
Inverter DC current at 12V, 24V and 48V
How watts, amps and volts are related
Electrical power in watts equals voltage in volts multiplied by current in amps. If you know any two of these, you can find the third. A device that uses 1200 watts at 12 volts draws 100 amps. The same device on a 24 volt supply draws only 50 amps.
This matters for inverters because the battery side carries a much higher current than the household side. A 1200W load at 120V AC draws about 10 amps from the wall, but the same load drawn from a 12V battery pulls 100 amps or more. That large current is why inverter cables must be thick and fused.
Quick formulas
Watts
Watts = Volts x Amps
Amps
Amps = Watts / Volts
Volts
Volts = Watts / Amps
Why inverter efficiency matters
An inverter is never 100 percent efficient. A typical one is 85 to 92 percent efficient, so it draws more power from the battery than it delivers to your devices. The second calculator includes this loss. For wiring and fuse sizing, use the cable and fuse calculator.
Frequently asked questions
How many amps is 1000 watts at 12 volts?
1000 divided by 12 is about 83 amps. With a typical 90 percent efficient inverter, the battery supplies about 93 amps.
Why does a higher battery voltage help?
The same power needs less current at a higher voltage. Half the current means thinner cables, less heat and less power lost.
What is the difference between AC amps and DC amps?
AC amps are on the household side of the inverter, usually at 120 volts. DC amps are on the battery side, where the voltage is lower, so the current is much higher.
Can I use this for solar panels?
Yes, the same formula applies. Divide the panel watts by the system voltage to estimate current.
Please note: This calculator uses simple electrical formulas. Real equipment varies, so always check the labels and manuals for your own gear.