4 AWG wire size
5.189 mm · 21.151 mm²
0.2043 in diameter · 0.815 Ω/km in copper · 70 A (NEC 60 °C copper)
What 4 AWG is used for
Ranges, subpanel feeders and heavy motor loads.
The numbers
| Diameter | 5.189 mm · 0.2043 in |
| Cross-sectional area | 21.1506 mm² |
| Resistance, copper | 0.815 Ω/km · 0.248 Ω per 1,000 ft |
| Resistance, aluminium | 1.333 Ω/km |
| NEC 60 °C copper ampacity | 70 A |
How 4 compares
The gauge scale is geometric, so the useful comparisons are ratios rather than differences. 1 AWG has twice the copper of 4 — 42.408 mm² against 21.151 — and therefore half the resistance per metre. 3/0 AWG is twice the diameter, which is four times the area.
| Gauge | Diameter | Area | Ω/km copper | vs 4 |
|---|---|---|---|---|
| 3/0 | 10.405 mm | 85.029 mm² | 0.2 | 4.02× the area |
| 2/0 | 9.266 mm | 67.431 mm² | 0.26 | 3.19× the area |
| 1/0 | 8.251 mm | 53.475 mm² | 0.32 | 2.53× the area |
| 1 | 7.348 mm | 42.408 mm² | 0.41 | 2.01× the area |
| 2 | 6.544 mm | 33.631 mm² | 0.51 | 1.59× the area |
| 3 | 5.827 mm | 26.67 mm² | 0.65 | 1.26× the area |
| 6 | 4.115 mm | 13.302 mm² | 1.3 | 0.63× the area |
| 8 | 3.264 mm | 8.366 mm² | 2.06 | 0.4× the area |
Frequently asked questions
What is 4 AWG in mm?
5.189 mm in diameter (0.2043 inches), with a cross-sectional area of 21.151 mm².
How many amps can 4 AWG copper carry?
70 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 4 AWG copper?
0.815 Ω per kilometre, or 0.248 Ω per 1,000 feet, for annealed copper at 20 °C. The same gauge in aluminium is about 1.33 Ω/km — 1.64 times higher, which is why aluminium wiring is sized larger for the same load.
How much thicker is 1 AWG than 4?
Three gauges lower is twice the cross-sectional area — 42.408 mm² against 21.151, a ratio of 2.005. That is not a coincidence: the AWG formula raises 92 to the power of (36−n)/39, and 92^(6/39) is 2.005.