Speaker wire gauge calculator
Wire gauge depends on three things: amplifier power, the final impedance (ohms) the amp sees, and how long the run is. Speaker size doesn’t matter.
Quick reference at 100 W
| Load | 10 ft | 25 ft | 50 ft | 100 ft |
|---|---|---|---|---|
| 8 Ω | 22 AWG | 18 AWG | 16 AWG | 12 AWG |
| 4 Ω | 20 AWG | 16 AWG | 12 AWG | 10 AWG |
| 2 Ω | 16 AWG | 12 AWG | 10 AWG | 6 AWG |
How we calculate it
We take the current at full rated power (the square root of watts divided by ohms), add up the resistance of the wire there and back, and pick the thinnest gauge that loses no more than 5% of the power (about 0.2 dB, which you can’t hear) and can carry the current. Copper values come from the standard AWG resistance table. Copper-clad aluminum is treated as 60% more resistive.
If you only know a “peak” or “max” wattage, enter it anyway. The answer will be thicker than needed, which is safe.
Running wire inside walls
Speaker wire inside walls or ceilings should be marked CL2 or CL3. Those ratings mean the jacket is tested to resist spreading fire, and in the US the electrical code calls for them in walls. CL3 covers higher power than CL2, so it is the safer pick for big amplifiers. The ampacity figures here are for open-air runs; wires bundled in a wall run warmer, so one size thicker is a sensible margin.
This calculator is for speaker wire only. A car amplifier’s power and ground cable and its fuse are sized differently. Follow the amplifier’s manual for those.