Wire Gauge Calculator
Minimum wire size for given current, distance, voltage, and acceptable drop.
About
Voltage drop = 2 × distance × current × resistance per metre. The calculator returns the smallest standard AWG that keeps drop under your chosen percentage of system voltage.
How it works
- Enter the maximum continuous current (use breaker rating, not average).
- Use one-way distance (the calculator doubles it for the return path).
- Most off-grid systems target ≤ 3% drop; battery-to-inverter runs target ≤ 1%.
Frequently asked questions
Why does 12 V need such thick wires?+
Power = volts × amps. To deliver 1,200 W at 12 V you need 100 A; at 48 V only 25 A. Cable cross-section scales with current, so doubling system voltage roughly halves the copper needed for the same power and acceptable drop.
What voltage drop is acceptable?+
≤ 3% on PV-to-controller and battery-to-load runs is the off-grid standard. ≤ 1% on battery-to-inverter is recommended because inverters draw very high amps and even small drops cause heat and tripping under surge.
AWG or mm²?+
Same property, different units. AWG is North American, mm² is metric. Conversion is non-linear: AWG 12 ≈ 3.3 mm², AWG 8 ≈ 8.4 mm², AWG 4 ≈ 21.2 mm². The calculator shows both.
Can I use aluminium instead of copper?+
Yes for high-current battery interconnects (forklift cable). Aluminium has ~60% the conductivity of copper, so size up by ~2 AWG to match. Use anti-oxidation paste at terminations and never mix Cu/Al at a screw lug without a transition plate.