AWG Wire Size Chart

The definition

d(n) = 0.005 × 92^((36 − n) / 39)   inch
area (cmil) = (d in mils)²
R = ρ × L / A     ρ_Cu = 1.7241×10⁻⁸ Ω·m (100% IACS), ρ_Al = 2.8264×10⁻⁸ Ω·m (61% IACS), at 20°C

Gauge numbers run backwards — 4/0 is the largest, 30 among the smallest — because the number originally counted drawing passes, not size.

Speaker wire: the 5% rule

For audio, the usual criterion is keeping wire resistance under 5% of the speaker's impedance, so damping factor stays intact. That is an impedance-matching judgment, not a safety rule, so it is independent of electrical code:

• 12 AWG into 8 Ω — up to 126 ft one way
• 14 AWG into 8 Ω — up to 79 ft one way
• 16 AWG into 8 Ω — up to 50 ft one way
• 18 AWG into 8 Ω — up to 31 ft one way

Halve those lengths for 4 Ω speakers.

Voltage drop

L_max = (V × %drop/100) / (2 × I × R_per_ft)

The factor of 2 is the return conductor — a mistake worth avoiding, since forgetting it makes every run look twice as good as it is.

Related charts

• Sheet metal gauge chart — the other gauge system, and why aluminum sheet uses this same AWG formula
• Pipe size chart — for conduit sizing alongside conductor sizing