Science & Units
AWG Wire Gauge Table
American Wire Gauge runs backwards and non-linearly, which is why it confuses everyone who meets it first. A larger number means a thinner wire: AWG 10 is thicker than AWG 22. And the steps are not equal — each gauge is a fixed ratio from the last, so the sequence is geometric rather than arithmetic.
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The ratio is exactly what makes the system useful. Thirty-nine steps span a factor of 92 in diameter, which means every six gauges doubles the diameter and every three gauges doubles the cross-section. That is why the resistance column roughly halves every three rows, and why electricians can estimate without a table: going from AWG 12 to AWG 9 doubles the copper.
The two anchor points define everything. AWG 36 is exactly 0.127 mm, and AWG 4/0 is exactly 11.684 mm. From those, the diameter of any gauge follows from d = 0.127 × 92^((36−n)/39). The cross-section is πd²/4, and the resistance is the resistivity of copper divided by that area.
One caution about what this table does not contain. Ampacity — how much current a wire can carry — cannot be calculated from cross-section alone. It depends on the insulation's temperature rating, whether the cable is in free air or bundled in a conduit, the ambient temperature, and how many current-carrying conductors share the raceway. Those figures come from tables in the electrical code, and they differ between countries. The resistance and voltage drop columns here are derived; the current ratings are not, and are deliberately left out.
AWG diameter and cross-section
| AWG | Diameter (mm) | Diameter (in) | Area (mm²) | Area (kcmil) |
|---|---|---|---|---|
| 0 | 8.2515 | 0.3249 | 53.4751 | 105.53 |
| 2 | 6.5437 | 0.2576 | 33.6308 | 66.37 |
| 4 | 5.1894 | 0.2043 | 21.1506 | 41.74 |
| 6 | 4.1154 | 0.1620 | 13.3018 | 26.25 |
| 8 | 3.2636 | 0.1285 | 8.3656 | 16.51 |
| 10 | 2.5882 | 0.1019 | 5.2612 | 10.38 |
| 12 | 2.0525 | 0.0808 | 3.3088 | 6.53 |
| 14 | 1.6277 | 0.0641 | 2.0809 | 4.11 |
| 16 | 1.2908 | 0.0508 | 1.3087 | 2.58 |
| 18 | 1.0237 | 0.0403 | 0.8230 | 1.62 |
| 20 | 0.8118 | 0.0320 | 0.5176 | 1.02 |
| 22 | 0.6438 | 0.0253 | 0.3255 | 0.64 |
| 24 | 0.5106 | 0.0201 | 0.2047 | 0.40 |
| 26 | 0.4049 | 0.0159 | 0.1288 | 0.25 |
| 28 | 0.3211 | 0.0126 | 0.0810 | 0.16 |
| 30 | 0.2546 | 0.0100 | 0.0509 | 0.10 |
| 32 | 0.2019 | 0.0080 | 0.0320 | 0.06 |
| 34 | 0.1601 | 0.0063 | 0.0201 | 0.04 |
| 36 | 0.1270 | 0.0050 | 0.0127 | 0.03 |
| 38 | 0.1007 | 0.0040 | 0.0080 | 0.02 |
| 40 | 0.0799 | 0.0031 | 0.0050 | 0.01 |
Every third gauge roughly halves the area: 10 is 5.26 mm², 13 would be 2.62, and 16 is 1.31. The rule of thumb is that three gauges double or halve the cross-section.
Copper resistance at 20 °C, derived from the cross-section
| AWG | Area (mm²) | Ohms per km | Ohms per 1,000 ft | Volts dropped at 10 A over 30 m |
|---|---|---|---|---|
| 0 | 53.475 | 0.322 | 0.098 | 0.193 |
| 2 | 33.631 | 0.513 | 0.156 | 0.308 |
| 4 | 21.151 | 0.815 | 0.248 | 0.489 |
| 6 | 13.302 | 1.296 | 0.395 | 0.778 |
| 8 | 8.366 | 2.061 | 0.628 | 1.236 |
| 10 | 5.261 | 3.277 | 0.999 | 1.966 |
| 12 | 3.309 | 5.210 | 1.588 | 3.126 |
| 14 | 2.081 | 8.285 | 2.525 | 4.971 |
| 16 | 1.309 | 13.173 | 4.015 | 7.904 |
| 18 | 0.823 | 20.947 | 6.385 | 12.568 |
| 20 | 0.518 | 33.306 | 10.152 | 19.984 |
| 22 | 0.326 | 52.959 | 16.142 | 31.775 |
| 24 | 0.205 | 84.208 | 25.667 | 50.525 |
| 26 | 0.129 | 133.897 | 40.812 | 80.338 |
| 28 | 0.081 | 212.904 | 64.893 | 127.742 |
| 30 | 0.051 | 338.530 | 103.184 | 203.118 |
Resistance is resistivity divided by area, so it doubles when the area halves. The last column counts the round trip: 30 m out and 30 m back, at 10 A.
What each gauge is normally used for
| AWG | Area (mm²) | Typical use |
|---|---|---|
| 18 | 0.82 | Thermostat wire, low-voltage signal |
| 16 | 1.31 | Speaker cable, short low-current runs |
| 14 | 2.08 | 15 A lighting circuits in North America |
| 12 | 3.31 | 20 A receptacle circuits, 20 A extension cords |
| 10 | 5.26 | 30 A circuits, solar panel strings |
| 8 | 8.37 | 40 A feeds, electric range branch |
| 6 | 13.30 | 50 A feeds, subpanels, EV chargers |
| 4 | 21.15 | 60 to 70 A service feeders |
| 2 | 33.63 | 100 A service entrance |
| 0 | 53.48 | 150 to 200 A service entrance |
These are conventional uses, not ratings. The actual permitted current depends on insulation temperature rating, how the cable is run, and how many conductors share a conduit.
Metric cable sizes and the nearest AWG
| Metric (mm²) | Nearest AWG | AWG area (mm²) | Difference |
|---|---|---|---|
| 0.50 | 20 | 0.518 | 3.5% |
| 0.75 | 18 | 0.823 | 9.7% |
| 1.00 | 17 | 1.038 | 3.8% |
| 1.50 | 15 | 1.650 | 10.0% |
| 2.50 | 13 | 2.624 | 5.0% |
| 4.00 | 11 | 4.172 | 4.3% |
| 6.00 | 9 | 6.634 | 10.6% |
| 10.00 | 7 | 10.549 | 5.5% |
| 16.00 | 5 | 16.773 | 4.8% |
| 25.00 | 3 | 26.670 | 6.7% |
| 35.00 | 2 | 33.631 | -3.9% |
| 50.00 | 0 | 53.475 | 7.0% |
| 70.00 | 0 | 53.475 | -23.6% |
| 95.00 | 0 | 53.475 | -43.7% |
European cable is sold by cross-section and North American by gauge, so a 2.5 mm² cable is closest to AWG 13 — a size that does not exist. Installers use AWG 14 or 12 and accept the small mismatch.
How to Use These Tables
- Reading a gauge: AWG 12 is 2.053 mm across and 3.31 mm². AWG 22 is 0.644 mm and 0.326 mm², ten times thinner in area.
- Estimating resistance: divide 17.24 by the area in mm² to get ohms per kilometre. AWG 10 at 5.26 mm² gives 3.28 Ω/km.
- Checking voltage drop: multiply the loop resistance by the current. 20 m of AWG 12 carrying 15 A drops 2 × 0.02 × 5.21 × 15 = 3.1 V, which is 2.6% of 120 V.
- Matching metric cable: 2.5 mm² is closest to AWG 13, which does not exist. Use AWG 14 (2.08 mm²) for a slight derate or AWG 12 (3.31 mm²) for margin.
- Remembering the sequence: three gauges double the area, six gauges double the diameter, and ten gauges change the area by a factor of ten.
Common Questions
Why does a higher AWG number mean a thinner wire?
Because the scale was built on the number of drawing passes used to make the wire. More passes made it thinner, so the count went up as the wire got smaller. The convention stuck when the manufacturing method changed.
Is AWG the same as mm²?
No, but they convert. AWG is a gauge number tied to a geometric series; mm² is an actual area. AWG 10 is 5.26 mm², and 6 mm² is closest to AWG 9, which is not a standard size.
How much current can AWG 12 carry?
It depends on the insulation and installation. In North America, 12 AWG copper with 60 °C insulation is rated 20 A in a typical branch circuit, and 25 A with 75 °C insulation. Both figures come from code tables, not from the cross-section.
What is a circular mil?
A unit of area equal to the area of a circle one thousandth of an inch across. It is defined as the diameter squared in mils, without the π/4 factor, which makes the arithmetic easier for round wires.
Why does resistance double every three gauges?
Because three gauges double the cross-section, and resistance is inversely proportional to area. The exact ratio is 92^(3/39) = 1.19 in diameter per gauge, which compounds to 2.0 over three steps.
What gauge is 2.5 mm² cable?
It falls between AWG 14 at 2.08 mm² and AWG 12 at 3.31 mm², closest to the non-standard AWG 13 at 2.62 mm². In practice installers choose AWG 14 when the load allows and AWG 12 when it does not.
More Science & Units
Sources
- ASTM B258 — Standard specification for standard nominal diameters of AWG sizes — ASTM International
- NEC Article 310 — Conductors for general wiring, ampacities — National Fire Protection Association
- IEC 60228 — Conductors of insulated cables, metric cross-sections — International Electrotechnical Commission
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