The smallest wire that keeps voltage drop in check for a 12-volt circuit, based on how much current it carries and how far it runs.
| Gauge | Voltage drop | Percent |
|---|
This checks voltage drop only. Also confirm the wire's ampacity for its insulation and where it runs, and fuse the circuit to protect the wire.
Copper wire resistance is standard for each AWG size. The length is doubled because current travels out to the load and back through the ground. The calculator then picks the smallest gauge that keeps the drop under your limit.
A 3% limit is the usual target for anything where voltage matters, like lighting, ignition and fuel pumps. Noncritical accessories can tolerate up to about 10%.
Resistance values are standard AWG copper figures at room temperature.