Wire Size Calculator

Wire it up right

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What wire gauge do I need for 20 amps?

For a typical short DC run, 20 amps calls for roughly 10 or 12 AWG copper, but the right wire gauge for amps depends on your cable length and voltage. Longer runs need thicker wire to hold voltage drop in check, so always run your exact amps and distance through a wire size calculator before you buy.

Why does voltage drop matter in an off-grid system?

In off-grid DC wiring every volt is precious. Excess voltage drop wastes battery power as heat, dims lights, and can stop chargers and inverters from working correctly. Keeping drop under about 3% means your gear gets the voltage it was designed for and undersized wire does not become a fire hazard.

How does cable distance affect wire size?

Voltage drop grows with distance because resistance adds up over the full round-trip length of the run. Double the distance and you roughly double the drop, so a long cable run needs a thicker, lower-gauge wire than a short one carrying the same amps. This is why a wire size calculator asks for one-way run length.

Why does 12V need thicker wire than 120V?

Power equals volts times amps, so delivering the same watts at 12V pulls ten times the current of 120V. More amps means more heat and more voltage drop, which is why low-voltage off-grid DC wiring needs much thicker wire gauge for the same load than a household 120V AC circuit.