What cable gauge do I need for speaker cables?

Using the common 5% rule (cable resistance no more than 5% of the speaker impedance) at 8 ohms, this calculator returns: 18 AWG up to about 9.5m; 16 AWG to 15m; 14 AWG to 24m; 12 AWG to 38m. For a more conservative real-world install (keeping cable resistance to roughly 2-3% of the impedance) go one gauge thicker — e.g. 14 AWG up to 15m, 12 AWG to 20m, 10 AWG to 30m. For 4-ohm loads, go one gauge thicker again, since the same cable resistance is a larger fraction of a lower impedance.

AWG (American Wire Gauge) is a standardised system for wire sizes. Lower numbers mean thicker wire. Each 3-gauge reduction doubles the cross-sectional area and halves the resistance. Common speaker cable gauges are 12-18 AWG.

Can I use thicker cable than recommended?

Yes, thicker cable always reduces loss. The only downsides are cost, weight and flexibility. There is no electrical downside to using thicker cable. However, beyond a certain point the improvement is negligible.

Does cable quality matter beyond gauge?

For speaker cables, gauge (and therefore resistance) is by far the most important factor. The conductor material (oxygen-free copper vs standard copper) makes a negligible difference at audio frequencies. Good insulation and durable connectors are more important than exotic materials.

AudioCalcs

Cable Gauge Calculator — AWG for Speaker Cables

Calculate required cable gauge (AWG) for speaker cables based on length and impedance.

Cable Length (one way)

One-way run from amplifier to speaker; the calculator doubles it for the return conductor.

Speaker Impedance

Electrical impedance in ohms

Max Cable Resistance (% of impedance)

Gauge is selected so cable resistance stays below this percentage of the speaker impedance (the classic 5% rule)

How We Calculate This

Maximum Resistance

Max R = (Max Cable Resistance % / 100) × Speaker Impedance

The gauge is chosen so cable resistance stays below this fraction of the speaker impedance (the classic 5% rule). Note the displayed load-power loss is roughly twice this resistance fraction for small losses, so a 5% resistance limit corresponds to up to about 9.3% displayed power loss.

Cable Resistance

R = Resistance per metre × Length × 2

Multiply by 2 for the round trip (positive and negative conductors).

Power Loss

The cable and speaker form a voltage divider, so the level reaching the speaker is the voltage ratio k = Z / (Z + R_cable).

Level loss (dB) = 20 × log₁₀(k) — a voltage quantity, hence 20·log not 10·log.

Power loss (%) = (1 − k²) × 100 — the reduction in power actually delivered to the speaker.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard formulas. Always verify results for critical applications.