Using the wrong cable is one of the most dangerous mistakes in an inverter installation. Thin cable gets hot, wastes power and can start a fire, while a missing fuse removes the last line of protection. This calculator shows a safe starting point.
Enter your inverter power, battery voltage and the cable length, and press the button. You will get the current, a suggested fuse size and the cable thickness in AWG.
Inverter cable and fuse size calculator
How the cable and fuse calculator works
The calculator first works out the current the battery must deliver. It divides the inverter watts by the battery voltage and by the inverter efficiency. For example, a 2000W inverter on a 12V battery at 85 percent efficiency draws about 196 amps. That is a very large current, which is why heavy loads on 12V need thick cable.
It then sizes the cable for 125 percent of that current and checks the voltage drop over the length you entered. Voltage drop is the power lost along the cable. We aim for no more than 3 percent, because a long or thin cable wastes power as heat and can make the inverter shut down on low voltage. The fuse is chosen at the next standard size above 125 percent of the current and should be fitted on the positive cable as close to the battery as possible.
Safety tips for inverter wiring
Always fit a fuse
A fuse or breaker protects the cable from fire if there is a short circuit. It must be rated for DC and fitted close to the battery terminal.
Keep cables short
Place the inverter as close to the battery as is safe. Halving the cable length halves the voltage drop and may let you use thinner cable.
Use a higher voltage for big inverters
The same 2000W at 24V draws about half the current of 12V, and at 48V about a quarter. Cables, fuses and losses all shrink. Our inverter size calculator suggests the battery voltage for your load.
Frequently asked questions
What size cable do I need for a 1000W inverter?
On a 12V battery a 1000W inverter draws around 98 amps, and our calculator suggests about 2 AWG for a short run. On 24V the current is half, so thinner cable is possible.
Where should the fuse go?
On the positive cable, as close to the battery as possible, and rated for DC current. It protects the whole cable run.
Why does the cable get thicker for longer runs?
Longer cable has more resistance, so more voltage is lost along it. A thicker cable keeps the voltage drop low.
Can I use a thinner cable if I only run the inverter briefly?
It is not safe to assume that. Size the cable for the inverter at full load, because the load can rise at any time.
Please note: This tool gives a conservative estimate and is not a substitute for your inverter manual, local electrical code or a qualified electrician. Always follow the manufacturer instructions.