Wire Gauge Calculator

Enter amp draw, one-way run length, and system voltage. The calculator finds the minimum AWG that keeps voltage drop inside your tolerance and checks it against an open-air ampacity table. Winches, light bars, dual battery, aux fuse blocks — same math.

Circuit specs

Amp draw

Continuous draw — use surge rating for winches (typically 300–500A)

One-way run length

feet — positive to load only; calculator doubles for return path

System voltage

Max voltage drop

Lower tolerance = heavier wire required

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AWG minimum for voltage drop

AWG	Ω / 1000 ft	Ampacity (open air)	Total Ω (2× run)	Volt drop	% drop	Pass?

How the math works

Voltage drop = current × total circuit resistance. Total resistance = wire resistance per foot × 2× the one-way run (power goes out and comes back). The minimum AWG is the smallest gauge whose resistance-per-foot keeps the drop inside your tolerance.

Ampacity is a separate check — the wire must handle the current without overheating. For most off-road accessories the voltage-drop calculation drives a heavier gauge than ampacity alone requires, so the ampacity check is a confirmation, not the primary constraint. The table assumes a single wire in open air. Pick the fuse separately: it protects the wire, so its rating should be at or below the wire’s.

These values use copper wire resistance at 68°F (20°C). Wire resistance increases ~0.4% per °F above that, which matters for underhood runs in hot climates. If your run spends time bundled in a hot loom, go one size heavier.