AWG Wire Gauge Calculator
Convert American Wire Gauge to diameter, cross-section area, kcmil and resistance — and reverse-look up the nearest AWG
Wire gauge
This ampacity is a documented reference value for common copper building wire, not a calculated result. The real allowable current depends on the applicable standard (NEC / IEC), insulation temperature rating, ambient temperature, bundling and installation method. Always verify with the code and a qualified electrician.
AWG wire gauge chart (4/0 – 40)
| AWG | Ø (mm) | Area (mm²) | Cu (Ω/km) | Amp. ref (A) |
|---|---|---|---|---|
| 4/0 | 11.684 | 107.2193 | 0.161 | ~230 |
| 3/0 | 10.405 | 85.0288 | 0.203 | ~200 |
| 2/0 | 9.266 | 67.4309 | 0.256 | ~175 |
| 1/0 | 8.251 | 53.4751 | 0.322 | ~150 |
| 1 | 7.348 | 42.4077 | 0.407 | ~130 |
| 2 | 6.544 | 33.6308 | 0.513 | ~115 |
| 3 | 5.827 | 26.6705 | 0.646 | ~100 |
| 4 | 5.189 | 21.1506 | 0.815 | ~85 |
| 5 | 4.621 | 16.7732 | 1.028 | — |
| 6 | 4.115 | 13.3018 | 1.296 | ~65 |
| 7 | 3.665 | 10.5488 | 1.634 | — |
| 8 | 3.264 | 8.3656 | 2.061 | ~50 |
| 9 | 2.906 | 6.6342 | 2.599 | — |
| 10 | 2.588 | 5.2612 | 3.277 | ~35 |
| 11 | 2.305 | 4.1723 | 4.132 | — |
| 12 | 2.053 | 3.3088 | 5.21 | ~25 |
| 13 | 1.828 | 2.624 | 6.57 | — |
| 14 | 1.628 | 2.0809 | 8.285 | ~20 |
| 15 | 1.45 | 1.6502 | 10.447 | — |
| 16 | 1.291 | 1.3087 | 13.173 | ~18 |
| 17 | 1.15 | 1.0378 | 16.611 | — |
| 18 | 1.024 | 0.823 | 20.947 | ~16 |
| 19 | 0.912 | 0.6527 | 26.413 | — |
| 20 | 0.812 | 0.5176 | 33.306 | ~11 |
| 21 | 0.723 | 0.4105 | 41.999 | — |
| 22 | 0.644 | 0.3255 | 52.959 | ~7 |
| 23 | 0.573 | 0.2582 | 66.78 | — |
| 24 | 0.511 | 0.2047 | 84.208 | ~3.5 |
| 25 | 0.455 | 0.1624 | 106.185 | — |
| 26 | 0.405 | 0.1288 | 133.897 | — |
| 27 | 0.361 | 0.1021 | 168.84 | — |
| 28 | 0.321 | 0.081 | 212.904 | — |
| 29 | 0.286 | 0.0642 | 268.467 | — |
| 30 | 0.255 | 0.0509 | 338.53 | — |
| 31 | 0.227 | 0.0404 | 426.879 | — |
| 32 | 0.202 | 0.032 | 538.284 | — |
| 33 | 0.18 | 0.0254 | 678.764 | — |
| 34 | 0.16 | 0.0201 | 855.905 | — |
| 35 | 0.143 | 0.016 | 1079.277 | — |
| 36 | 0.127 | 0.0127 | 1360.943 | — |
| 37 | 0.113 | 0.01 | 1716.117 | — |
| 38 | 0.101 | 0.008 | 2163.984 | — |
| 39 | 0.09 | 0.0063 | 2728.734 | — |
| 40 | 0.08 | 0.005 | 3440.87 | — |
Diameter, area and copper resistance are computed from the AWG definition at 20 °C. The ampacity column is a documented reference for common gauges only — see the disclaimer above.
About this tool
This AWG wire gauge calculator converts an American Wire Gauge number into its conductor diameter (in millimetres and inches), cross-sectional area (in mm² and kcmil) and DC resistance per kilometre for both copper and aluminum. It also works in reverse: enter a measured diameter or cross-section and it returns the closest standard AWG size. A full wire gauge chart from 4/0 down to AWG 40 highlights the selected row, and a scaled cross-section circle shows the relative conductor size. It is built for electricians, makers, audio and automotive wiring, and students who need fast, physically accurate gauge conversions.
How to use
- 1 Choose a mode: convert From AWG, or reverse-look up From size (diameter or area).
- 2 In From AWG mode, pick the gauge from the list (4/0 through 40); the cross-section preview updates instantly.
- 3 In From size mode, enter a measured diameter in mm or an area in mm² to get the nearest standard AWG.
- 4 Read the diameter, area, kcmil and copper/aluminum resistance, check the reference ampacity (with its disclaimer), and copy the result.
How it works
AWG uses a geometric ratio: the diameter is d = 0.127 · 92^((36 − n)/39) mm, where n is the gauge number and the "ought" sizes are negative (1/0 = 0, 2/0 = −1, 3/0 = −2, 4/0 = −3). The cross-sectional area is A = (π/4)·d². Circular mils come from cmil = (d / 0.0254 mm)², and 1 kcmil = 1000 cmil. The DC resistance per length is R/L = ρ / A, using resistivity at 20 °C of 1.724×10⁻⁸ Ω·m for copper and 2.82×10⁻⁸ Ω·m for aluminum, scaled to Ω/km. So AWG 12 is about 2.05 mm / 3.31 mm² with ≈5.21 Ω/km in copper, and 4/0 is about 11.68 mm / 107.2 mm². The reverse lookup simply finds the standard gauge whose diameter or area is closest to your value.
Frequently asked questions
What does the AWG number mean?
American Wire Gauge is a standardized scale where a larger number means a thinner wire. Each step down (e.g. 12 → 10) increases the cross-section by about 26%, and six steps roughly double the diameter. Very thick conductors are written with "ought" notation: 1/0, 2/0, 3/0 and 4/0 (also written 0, 00, 000, 0000), which this tool treats as gauge 0, −1, −2 and −3.
How do I convert AWG to mm² or kcmil?
Compute the diameter with d = 0.127 · 92^((36 − n)/39) mm, then the area A = (π/4)·d² in mm². For kcmil, convert the diameter to mils (1 mil = 0.0254 mm), square it for circular mils, and divide by 1000. This calculator does all of that automatically and also shows the inch diameter.
Why do copper and aluminum show different resistance?
Resistance per length is R/L = ρ / A. Copper has a lower resistivity (1.724×10⁻⁸ Ω·m) than aluminum (2.82×10⁻⁸ Ω·m), so for the same gauge aluminum has roughly 1.6× the resistance. That is why an aluminum conductor usually needs to be one or two AWG sizes larger to match copper for the same voltage drop.
Can I use the ampacity value to size a circuit?
Not on its own. The ampacity shown is a documented reference for common copper building wire — it is not calculated and does not account for your insulation temperature rating, ambient temperature, conductor bundling or installation method. Real current ratings come from the applicable standard (NEC table 310.16 or IEC) and must be confirmed by a qualified electrician.
Related tools and uses
Use this with the voltage drop calculator to size a wire run for an acceptable drop, the Ohm's law calculator for V, I, R and power, and the resistor color code calculator for component values.