Enter your current, run length and voltage. We'll size the cable to keep voltage drop under your target — not just to match the amp rating.
This sizes for voltage drop, which for solar DC wiring is usually the limiting factor over ampacity/heat — always check your cable's ampacity rating too, and follow local electrical code.
Further reading: Off-Grid Solar 101: What It Actually Takes to Leave the Grid
The "2×" accounts for the round trip — current has to travel out to the load and back through the return conductor. This is the same core formula electricians and solar installers use for a first-pass cable sizing check; it's then rounded up to the nearest standard commercial cable size, since cable doesn't come in arbitrary cross-sections.
Ampacity tables assume a short run. Over a long distance at low DC voltage, resistance losses can push voltage drop well past 3% long before you hit the cable's heat-based amp limit — voltage drop is usually the binding constraint for solar wiring runs.
3% is a common overall system target (sometimes split as 1% panel-to-controller and 2% controller-to-battery). Critical, high-current short runs sometimes target 1-2% to minimize losses.