How it works
AWG is a logarithmic scale: every 6 gauges halves the diameter, and a smaller AWG number means a thicker wire. Gauges 0 to 0000 (written 1/0 to 4/0) are entered here as 0, −1, −2 and −3.
Resistance per metre uses annealed copper at 20 °C (1.724 × 10⁻⁸ Ω·m). Use it to estimate voltage drop: multiply by the total wire length, there and back.
d (mm) = 0.127 × 92^((36 − AWG) / 39)
A (mm²) = π/4 × d²
R (Ω/m) = 1.724e-8 / A(m²)Worked example
18 AWG has a diameter of 0.127 × 92^(18/39) = 1.024 mm, an area of 0.823 mm² and about 20.9 mΩ per metre, so a 5 m run there and back (10 m) has roughly 0.21 Ω.