AWG sizes and wire diameter
American Wire Gauge is the standard way of sizing solid, round, electrically conducting wire in North America. The numbering runs backwards: the larger the gauge number, the thinner the wire. Sizes thicker than 0 are written as 1/0, 2/0, 3/0 and 4/0, also known as 0, 00, 000 and 0000.
The formula
AWG is defined so that 36 AWG is 0.005 inches across and 0000 AWG is 0.46 inches, with 39 equal steps on a logarithmic scale between them. For a gauge n:
diameter (mm) = 0.127 × 92^((36 − n) ÷ 39)
Two handy rules follow from this. Every 6 gauges halves (or doubles) the diameter, and every 3 gauges roughly halves (or doubles) the cross-section area and therefore doubles (or halves) the resistance.
Common sizes
| AWG | Diameter (mm) | Diameter (in) | Area (mm²) | Copper Ω/km |
|---|---|---|---|---|
| 4/0 | 11.68 | 0.4600 | 107 | 0.161 |
| 2/0 | 9.266 | 0.3648 | 67.4 | 0.256 |
| 1/0 | 8.251 | 0.3249 | 53.5 | 0.322 |
| 2 | 6.544 | 0.2576 | 33.6 | 0.513 |
| 4 | 5.189 | 0.2043 | 21.2 | 0.815 |
| 6 | 4.115 | 0.1620 | 13.3 | 1.3 |
| 8 | 3.264 | 0.1285 | 8.37 | 2.06 |
| 10 | 2.588 | 0.1019 | 5.26 | 3.28 |
| 12 | 2.053 | 0.0808 | 3.31 | 5.21 |
| 14 | 1.628 | 0.0641 | 2.08 | 8.29 |
| 16 | 1.291 | 0.0508 | 1.31 | 13.2 |
| 18 | 1.024 | 0.0403 | 0.823 | 20.9 |
| 20 | 0.8118 | 0.0320 | 0.518 | 33.3 |
| 22 | 0.6438 | 0.0253 | 0.326 | 53 |
| 24 | 0.5106 | 0.0201 | 0.205 | 84.2 |
| 26 | 0.4049 | 0.0159 | 0.129 | 134 |
| 28 | 0.3211 | 0.0126 | 0.081 | 213 |
| 30 | 0.2546 | 0.0100 | 0.0509 | 339 |
Resistance
Resistance figures assume solid annealed copper at 20 °C (resistivity 0.017241 Ω·mm²/m). Resistance rises about 0.39% per °C, so warm wire measures higher. Aluminium has roughly 1.6 times the resistance of copper for the same size, which is why aluminium cable is usually two gauges larger for the same job.
Current ratings
There is no single safe current for a wire size. It depends on how hot the insulation may get, whether the wire is bundled or in conduit, the ambient temperature and how much voltage drop you can accept. The three figures shown are common references:
- Building wire (NEC 60 °C): the US National Electrical Code ampacity for copper conductors with 60 °C insulation, as used for household circuits. 14 AWG is 15 A and 12 AWG is 20 A.
- Chassis wiring: a widely quoted rule of thumb for a single short wire in open air inside equipment.
- Power transmission: a conservative 700 circular mils per amp, suitable for bundled cables and long runs.
For mains wiring, always follow your local electrical code rather than any table.
Stranded wire and metric sizes
Stranded wire of a given gauge has about the same copper area as the solid wire, but a slightly larger overall diameter because of the gaps between strands. Outside North America cable is sold by cross-section area in mm² (1.5, 2.5, 4 mm² and so on). Use the lookup above to find the matching or next larger AWG.
