Enter the load and one-way distance; get the smallest real conductor that passes both the drop budget and the ampacity check on a 48 V system.
48 V dominates modern off-grid solar, server/telecom DC plants and golf carts — the highest DC voltage that stays in the touch-safe class while cutting copper to one-sixteenth of the 12 V equivalent.
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 · 48V 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% × 48 V = 1.44 V; R(max) = 1.44 × 1000 ÷ (2 × 40 × 30) = 0.600 Ω/kft; smallest gauge under that with ampacity ≥ 40 A is 6 AWG (0.491 Ω/kft, 65 A). Actual drop: 1.18 V = 2.46%.
Roughly 125 A at full output: 1/0 copper at very short runs (≤6 ft one-way, 3%), 2/0 beyond. Keep inverter cables brutally short.
It sits at the top of the conventionally touch-safe band (SELV limits are 60 V DC), but arcing and energy are very real — fuse every battery conductor and torque every lug.