8 AWG wire size
3.264 mm · 8.366 mm²
0.1285 in diameter · 2.061 Ω/km in copper · 40 A (NEC 60 °C copper)
What 8 AWG is used for
40-amp circuits — ranges, larger air conditioners, EV chargers.
The numbers
| Diameter | 3.264 mm · 0.1285 in |
| Cross-sectional area | 8.3656 mm² |
| Resistance, copper | 2.061 Ω/km · 0.628 Ω per 1,000 ft |
| Resistance, aluminium | 3.371 Ω/km |
| NEC 60 °C copper ampacity | 40 A |
How 8 compares
The gauge scale is geometric, so the useful comparisons are ratios rather than differences. 2 AWG is twice the diameter, which is four times the area.
| Gauge | Diameter | Area | Ω/km copper | vs 8 |
|---|---|---|---|---|
| 2 | 6.544 mm | 33.631 mm² | 0.51 | 4.02× the area |
| 3 | 5.827 mm | 26.67 mm² | 0.65 | 3.19× the area |
| 4 | 5.189 mm | 21.151 mm² | 0.82 | 2.53× the area |
| 6 | 4.115 mm | 13.302 mm² | 1.3 | 1.59× the area |
| 10 | 2.588 mm | 5.261 mm² | 3.28 | 0.63× the area |
| 12 | 2.053 mm | 3.309 mm² | 5.21 | 0.4× the area |
| 14 | 1.628 mm | 2.081 mm² | 8.28 | 0.25× the area |
Frequently asked questions
What is 8 AWG in mm?
3.264 mm in diameter (0.1285 inches), with a cross-sectional area of 8.366 mm².
How many amps can 8 AWG copper carry?
40 A under the NEC 60 °C copper column, which is the figure that sets the breaker on an ordinary branch circuit. This is a starting point and not a permission: the real limit depends on insulation rating, ambient temperature, how many conductors share the run, and your local code.
What is the resistance of 8 AWG copper?
2.061 Ω per kilometre, or 0.628 Ω per 1,000 feet, for annealed copper at 20 °C. The same gauge in aluminium is about 3.37 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.