12-Volt Wire Size Calculator

Your details

Nominal DC supply voltage. Most automotive and small solar systems are 12 V.
Choose amps if you know the draw from the device datasheet; choose watts if you only know the power rating.
Maximum continuous current drawn by the device or circuit.
A
Distance from the power source to the load. The calculator doubles this for the return conductor.
ft
3 % is standard for lighting and sensitive electronics. Up to 5 % is acceptable for motors and resistive loads.
%
Copper is standard in automotive, marine, and most DC wiring. Aluminum is used in some solar/battery cables.
Recommended wire gaugeExcellent - within 3%
8 AWG (8.37 mm²)

Smallest AWG that keeps voltage drop within your limit and stays within ampacity ratings.

Wire cross-section8.37mm²
Load current20A
Actual voltage drop0.251V
Voltage drop2.09%
Wire power loss5.02W
Suggested fuse rating25 A
Min. area (voltage drop)5.839mm²
2.09% %
Ideal (<2%)<2%Good (2-3%)2%-3%Acceptable (3-5%)3%-5%High (>5%)5%+

Use 8 AWG (8.37 mm²) for this circuit.

  • The wire drops 0.251 V (2.09%) across the full circuit at that gauge.
  • Power lost as heat in the wire is 5.02 W. Keeping runs short and wire large reduces this directly.
  • A 25 A fuse is recommended at the source end. Always fuse as close to the battery or bus as practical.
  • Doubling to a 24 V system for the same wattage halves the current and allows much smaller (cheaper) wire.

Next stepInstall the wire with proper crimp or lug terminations rated for the AWG and apply heat-shrink tubing over all connections.

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