Wire Gauge Calculator

It depends on the light bar's amp draw and how far it sits from your power source. Most full-size LED light bars pull anywhere from 6–20 amps — check your product's spec sheet for the exact figure, then run it through the calculator above with your wire length to get an exact recommendation.

AWG (American Wire Gauge) and mm² (square millimeters) are two different systems for measuring wire thickness. AWG is standard in the U.S. and gets smaller in number as the wire gets thicker (18 AWG is thin, 4 AWG is thick). mm² measures the actual cross-sectional area of the copper and is common internationally. Our calculator and reference chart use AWG, the standard for automotive and emergency vehicle wiring in the U.S.

One-way is the distance from your power source to the accessory. Round-trip accounts for both the power wire out and the ground/return wire back. If you're not sure which number you have, measure the one-way distance — it's the easiest to get accurately with a tape measure — and select "One-way distance" in the calculator.

Every foot of wire adds a small amount of resistance, and that resistance causes voltage to drop between your power source and your accessory. Longer runs lose more voltage, so they need a thicker wire (lower AWG number) to keep that drop within a safe range — even if the amp draw stays the same.

Undersized wire causes excess voltage drop, which can lead to dim lighting, weak siren output, or erratic electronics behavior. It also generates more heat than properly sized wire, which — especially in bundled or enclosed wiring runs — can pose a fire risk over time. When your calculated result falls between two sizes, always round up.

Not electrically — oversized wire is always safe from a performance standpoint. The only tradeoffs are cost, weight, and it being harder to route and terminate in tight spaces. When in doubt, sizing up is the safer choice.