Wire Sizing Calculator

Size DC and AC wiring by current, voltage and run length. Get the wire gauge that keeps voltage drop within range.

Wire Sizing (Voltage Drop)

Conductor size from voltage, current, run length and allowed drop — checked against both voltage drop and ampacity, whichever governs. Formula: A = 2·L·I·ρ ÷ V_drop, copper ρ = 1.72×10⁻⁸ Ω·m.

System voltage (V)

Current (A)

One-way run (m)

Max drop (%)

25 mm² (≈ 2 AWG)

Ampacity governs (drop alone would allow a smaller cable). Drop-only requirement: 8.2 mm².

Actual drop: 0.47 V (1.0%) · Cable loss: 33 W of heat at full current.

Round-trip drop is included (2× length). Keep DC battery runs under 3% drop; 5% is acceptable for non-critical circuits. Upsize one step for engine bays, conduit, or ambient above 30°C, and protect every run with the correctly sized fuse/breaker (see Circuit Protection panel).