What the wire gauge reference covers
The AWG table lists every American Wire Gauge size from 4/0 to 40 with diameter in inches and millimetres, cross-sectional area in mm² and kcmil, and the DC resistance of solid annealed copper at 20 °C. It also gives the British Standard Wire Gauge (SWG) diameters, because the same gauge number means a different size in the two systems.
The tables describe the conductor itself. They do not give ampacity: the current a wire may carry depends on its insulation rating, installation method, bundling and the electrical code that applies, so check the code, or use the voltage drop calculator for a specific run.
Common building-wire sizes at a glance
The sizes most often used for branch circuits, feeders and appliance runs, with solid-conductor resistance for copper (100% IACS) and aluminum (1350 alloy, 61% IACS) at 20 °C.
| AWG | Diameter (mm) | Area (mm²) | Copper Ω/km | Aluminum Ω/km |
|---|---|---|---|---|
| 14 | 1.628 | 2.08 | 8.285 | 13.583 |
| 12 | 2.053 | 3.31 | 5.211 | 8.542 |
| 10 | 2.588 | 5.26 | 3.277 | 5.372 |
| 8 | 3.264 | 8.37 | 2.061 | 3.379 |
| 6 | 4.115 | 13.30 | 1.296 | 2.125 |
| 4 | 5.189 | 21.15 | 0.815 | 1.336 |
| 2 | 6.544 | 33.63 | 0.513 | 0.840 |
| 1/0 | 8.251 | 53.48 | 0.322 | 0.529 |
Rules of thumb from the AWG definition
Because AWG is a geometric series, a few ratios hold at every size. They follow directly from the definition, so they are exact up to rounding.
- One gauge step changes the diameter by a factor of 1.1229 (about 12.3%) and the area by 1.2610 (about 26.1%).
- Three gauge steps change the area, and so the resistance, by a factor of 2.005: 3 AWG sizes thicker is about half the resistance.
- Six gauge steps change the diameter by the same factor of 2.005, and ten steps change the area by 10.16.
- Aluminum 1350 has 1.64 times the resistivity of annealed copper, so an aluminum conductor must be about two AWG sizes larger for similar resistance.
- Copper resistance rises about 0.393% per °C, so a conductor at 75 °C has about 22% more resistance than the 20 °C values in these tables.