Wire size
Pick a wire that won't cook or starve the load
Enter the current, the system voltage, and how far the wire runs. You get the gauge, the voltage that actually reaches the load, and the fuse to protect it.
Table and formula from the original megawattrv.com calculator
Recommended wire
6 AWG
of allowed drop used
How the math works
The original Megawatt tool uses a published table for 105°C copper. It finds the smallest wire that clears two tests at once.
First, size. Circular mils needed = 10.75 × amps × one-way feet × 2, divided by the volts you can afford to lose. Second, heat. The wire's rated amps, cut down for engine-bay heat and bundling, has to cover the load.
The fuse starts at 125% of the load and steps up to the next standard size. If that would be bigger than the wire can safely carry, it drops back to the wire's limit.
Where people go wrong
They measure one way and forget the current comes back. Or they bundle six wires in a loom and use the open-air rating. Both make a wire run warmer than the table promised.