Enter the load and one-way distance; get the smallest real conductor that passes both the drop budget and the ampacity check on a 24 V system.
24 V is the sweet spot for serious trolling motors and mid-size off-grid systems: same power as 12 V at half the current, which means one-quarter of the copper for the same percentage drop.
Generic wire-size tools solve ρ·L/A and report a theoretical gauge — famously including sizes like "13 AWG" that don't exist at the supply house, with no check that the wire can carry the current thermally. This calculator returns only real, purchasable conductors, enforces the NEC ampacity floor for the load, applies the drop budget, and shows the verdict — wire you can actually buy and legally install. Every result comes with the fan chart, upgrade economics, and a PDF report.
Siblings: DC wire size hub · 24V voltage drop (check an existing wire) · metric sizes.
| Vd(max) | budget volts = limit% × source voltage |
| Rmax | largest acceptable resistance, Ω/kft |
| answer | smallest gauge with R ≤ Rmax and Table 310.16 ampacity ≥ I |
Two gates, not one: a gauge must pass the drop budget AND carry the current thermally. Physics-only calculators stop at the first gate.
Work it in three lines: budget = 3% × 24 V = 0.72 V; R(max) = 0.72 × 1000 ÷ (2 × 48 × 25) = 0.300 Ω/kft; smallest gauge under that with ampacity ≥ 48 A is 3 AWG (0.245 Ω/kft, 100 A). Actual drop: 0.59 V = 2.45%.
A typical 48 A motor needs 3 AWG copper at a strict 3% budget (6 AWG lands at 4.9% — the common 5%-class pick), versus 1/0 if it were a 12 V system. That difference is the entire argument for 24 V.
Half the current for the same watts AND double the voltage base for the percentage: the two effects multiply to a 4× advantage in allowable resistance.