How much level and power your speaker or sub wire loses: length, gauge and ohm load in, dB and % lost out.
Wire length, amp to speaker (ft)
One way. The trip back is counted for you.
Wire gauge (AWG)
18
16
14
12
10
8
18
16
14
12
10
8
Wire
Copper
(OFC)
CCA
(aluminum)
Copper (OFC)
CCA (aluminum)
Copper (OFC)
CCA (aluminum)
Load (Ω)
The speaker, or the sub’s final load.
Lost in the wire
0.34 dB · 3.9 %
Wire resistance, out and back
0.161 Ω
Thinnest for under 5 % loss
16 AWG
Formula
R = 2 × L × Ω/ft, loss = 20 × log₁₀((Z + R) ÷ Z)
With
L = 20 ft, 16 AWG = 4.015 Ω / 1,000 ft, Z = 4 Ω
Guidance only, never a safety rating. Follow your amp and vehicle manuals. The fuse protects the wire: put it within 18 in of the battery. Disconnect the battery before you wire.
How it works
Enter how long the run is from the amp to the speaker (one way), the wire gauge and the load in ohms. You get the level lost in dB, the share of the power that heats the wire, and the thinnest gauge that keeps it under 5 %.
Example: 20 ft of 16 AWG copper is 2 × 20 × 0.004015 = 0.161 Ω out and back. To a 4 Ω speaker that loses 20 × log₁₀(4.161 ÷ 4) = 0.34 dB, or 3.9 % of the power.
The same 20 ft to a 1 Ω sub load loses 1.29 dB, 13.8 % of the power. 10 AWG brings it down to 3.8 %: the lower the load, the thicker the wire.
Frequently asked questions
What gauge speaker wire for a sub?
It depends on the load and the length. For a 1 Ω load 20 ft from the amp, 10 AWG keeps the loss under 5 %; 16 AWG would waste 13.8 % of the power.
Why does the length count twice?
The current goes out to the speaker on one wire and comes back on the other, so 20 ft of speaker cable is 40 ft of wire in the circuit.
Is CCA speaker wire OK?
It works if you go thicker. CCA has about 1.6 × the resistance of copper: 20 ft of 16 AWG CCA to 4 Ω loses 6.0 % instead of 3.9 %.