| Gauge (AWG) | Voltage Drop | Within Limit? |
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How to Size DC Wire
On a low-voltage DC circuit, the right wire gauge is set by voltage drop, not just how much current it can carry. As current travels out to the load and back, the wire’s resistance bleeds off voltage. Pick a gauge thick enough to keep that drop within an acceptable limit over your run length, and the load gets the voltage it needs.
Why Voltage Drop Matters at 12 Volts
At 12 volts there is little headroom, so even a small drop is a big percentage. A half-volt lost is over four percent at 12V but only one percent at 48V. That is why long 12V runs — winches, lights, fridges, audio — need surprisingly thick wire, and why higher-voltage systems can use thinner conductors for the same job.
Round-Trip Length
DC current has to flow out to the device and back through the ground or return wire, so the resistance that matters is twice your one-way distance. This calculator already doubles your length, which is why a 10-foot run is treated as 20 feet of conductor.
Fusing and Ampacity
Voltage drop sets the minimum gauge for performance, but the wire must also handle the current without overheating, and the fuse protects the wire from a short. Size the fuse to the wire, not just the load, and never up-fuse a circuit beyond what its wire can safely carry.
Frequently Asked Questions
What voltage drop is acceptable?
Three percent or less for critical loads like winches and audio amplifiers; up to ten percent is often fine for general lighting and accessories.
Does length really matter that much?
Yes. Voltage drop is directly proportional to length, so doubling the run distance doubles the drop and usually means going up a gauge or two.
Copper or aluminum?
Copper carries more current per size and is standard for automotive wiring. Aluminum needs roughly two gauges larger for the same performance.