18 AWG wire size
1.024 mm · 0.823 mm²
0.0403 in diameter · 20.947 Ω/km in copper
What 18 AWG is used for
Lamp cord, doorbells, thermostats and low-voltage control wiring.
The numbers
| Diameter | 1.024 mm · 0.0403 in |
| Cross-sectional area | 0.823 mm² |
| Resistance, copper | 20.947 Ω/km · 6.385 Ω per 1,000 ft |
| Resistance, aluminium | 34.263 Ω/km |
| NEC 60 °C copper ampacity | — outside the common building-wire range |
How 18 compares
The gauge scale is geometric, so the useful comparisons are ratios rather than differences. 12 AWG is twice the diameter, which is four times the area.
| Gauge | Diameter | Area | Ω/km copper | vs 18 |
|---|---|---|---|---|
| 12 | 2.053 mm | 3.309 mm² | 5.21 | 4.02× the area |
| 14 | 1.628 mm | 2.081 mm² | 8.28 | 2.53× the area |
| 16 | 1.291 mm | 1.309 mm² | 13.17 | 1.59× the area |
| 20 | 0.812 mm | 0.518 mm² | 33.31 | 0.63× the area |
| 22 | 0.644 mm | 0.326 mm² | 52.96 | 0.4× the area |
| 24 | 0.511 mm | 0.205 mm² | 84.21 | 0.25× the area |
Frequently asked questions
What is 18 AWG in mm?
1.024 mm in diameter (0.0403 inches), with a cross-sectional area of 0.823 mm².
Is 18 AWG used for power wiring?
Not for building circuits. It is a signal and low-current gauge — thinner than anything a domestic branch circuit uses.
What is the resistance of 18 AWG copper?
20.947 Ω per kilometre, or 6.385 Ω per 1,000 feet, for annealed copper at 20 °C. The same gauge in aluminium is about 34.26 Ω/km — 1.64 times higher, which is why aluminium wiring is sized larger for the same load.
Why do smaller AWG numbers mean thicker wire?
The number counts drawing operations. Wire is pulled through progressively smaller dies, and the gauge records how many passes it took — so more passes means a higher number and a thinner wire.