American Wire Gauge (AWG) Standardized Measurement System
Copper wire gauge is a standardized way to measure the thickness of a wire, defined by the American Wire Gauge (AWG) system. The lower the gauge number, the thicker the wire. Gauge determines how much current a conductor can safely carry, which makes it one of the first specs to get right in any cable.
Mercury Wire works across a wide range of copper gauges and copper types, including bare, tinned, and oxygen-free copper, for wire and cable built to suit demanding applications. The table below summarizes the gauges we work with most often, along with their key characteristics.
Gauge is one spec among many in a cable built to survive a real environment. If you need a copper type or gauge not listed here, or you are working on a custom cable where conductor size is only the starting point, our engineers can size and build the full assembly. Speak with an engineer.
Copper Wire Gauge Calculator
Select an AWG size for diameter, cross-sectional area, resistance, conductor weight, and ampacity under each of the three rating bases.
Conductor dimensions & resistance
Ampacity by rating basis (amps)
There is no single “max current” for a wire gauge. NEC values are Table 310.16 for not more than three current-carrying conductors in a raceway or cable at 30 °C ambient; apply the code’s temperature and bundling factors, and note that termination ratings (NEC 110.14(C)) usually limit you to the 75 °C column. Free air is a lone conductor with unrestricted airflow. The 700 cmil/A figure is a very conservative long-run rule of thumb, not an NEC value. Dimensions and resistance are for solid, bare annealed copper at 10.371 Ω·cmil/ft, 20 °C. This is a general engineering reference, not a substitute for the NEC or a licensed electrician.
| Gauge (AWG) | Diameter (in) | Diameter (mm) | Area (mm²) | Area (cmil) | Resistance @ 20°C (Ω/kft) | Resistance @ 75°C (Ω/kft) | Weight (lb/kft) |
|---|---|---|---|---|---|---|---|
| 4/0 | 0.4600 | 11.684 | 107 | 211,600 | 0.04901 | 0.05961 | 640.5 |
| 3/0 | 0.4096 | 10.405 | 85.0 | 167,806 | 0.06180 | 0.07516 | 507.9 |
| 2/0 | 0.3648 | 9.266 | 67.4 | 133,077 | 0.07793 | 0.09478 | 402.8 |
| 1/0 | 0.3249 | 8.251 | 53.5 | 105,535 | 0.09827 | 0.1195 | 319.4 |
| 1 | 0.2893 | 7.348 | 42.4 | 83,693 | 0.1239 | 0.1507 | 253.3 |
| 2 | 0.2576 | 6.544 | 33.6 | 66,371 | 0.1563 | 0.1900 | 200.9 |
| 3 | 0.2294 | 5.827 | 26.7 | 52,635 | 0.1970 | 0.2396 | 159.3 |
| 4 | 0.2043 | 5.189 | 21.2 | 41,741 | 0.2485 | 0.3022 | 126.3 |
| 5 | 0.1819 | 4.621 | 16.8 | 33,102 | 0.3133 | 0.3810 | 100.2 |
| 6 | 0.1620 | 4.115 | 13.3 | 26,251 | 0.3951 | 0.4805 | 79.46 |
| 7 | 0.1443 | 3.665 | 10.5 | 20,818 | 0.4982 | 0.6058 | 63.02 |
| 8 | 0.1285 | 3.264 | 8.37 | 16,510 | 0.6282 | 0.7640 | 49.97 |
| 9 | 0.1144 | 2.906 | 6.63 | 13,093 | 0.7921 | 0.9633 | 39.63 |
| 10 | 0.1019 | 2.588 | 5.26 | 10,383 | 0.9988 | 1.215 | 31.43 |
| 11 | 0.0907 | 2.305 | 4.17 | 8,234 | 1.260 | 1.532 | 24.92 |
| 12 | 0.0808 | 2.053 | 3.31 | 6,530 | 1.588 | 1.932 | 19.77 |
| 13 | 0.0720 | 1.828 | 2.62 | 5,178 | 2.003 | 2.436 | 15.68 |
| 14 | 0.0641 | 1.628 | 2.08 | 4,107 | 2.525 | 3.071 | 12.43 |
| 15 | 0.0571 | 1.450 | 1.65 | 3,257 | 3.184 | 3.873 | 9.858 |
| 16 | 0.0508 | 1.291 | 1.31 | 2,583 | 4.015 | 4.883 | 7.818 |
| 17 | 0.0453 | 1.150 | 1.04 | 2,048 | 5.063 | 6.158 | 6.200 |
| 18 | 0.0403 | 1.024 | 0.823 | 1,624 | 6.385 | 7.765 | 4.917 |
| 19 | 0.0359 | 0.912 | 0.653 | 1,288 | 8.051 | 9.791 | 3.899 |
| 20 | 0.0320 | 0.812 | 0.518 | 1,022 | 10.15 | 12.35 | 3.092 |
| 21 | 0.0285 | 0.723 | 0.410 | 810.1 | 12.80 | 15.57 | 2.452 |
| 22 | 0.0253 | 0.644 | 0.326 | 642.4 | 16.14 | 19.63 | 1.945 |
| 23 | 0.0226 | 0.573 | 0.258 | 509.5 | 20.36 | 24.76 | 1.542 |
| 24 | 0.0201 | 0.511 | 0.205 | 404.0 | 25.67 | 31.22 | 1.223 |
| 25 | 0.0179 | 0.455 | 0.162 | 320.4 | 32.37 | 39.36 | 0.9699 |
| 26 | 0.0159 | 0.405 | 0.129 | 254.1 | 40.81 | 49.64 | 0.7692 |
| 27 | 0.0142 | 0.361 | 0.102 | 201.5 | 51.47 | 62.59 | 0.6100 |
| 28 | 0.0126 | 0.321 | 0.0810 | 159.8 | 64.90 | 78.92 | 0.4837 |
| 29 | 0.0113 | 0.286 | 0.0642 | 126.7 | 81.83 | 99.52 | 0.3836 |
| 30 | 0.0100 | 0.255 | 0.0509 | 100.5 | 103.2 | 125.5 | 0.3042 |
| 31 | 0.00893 | 0.227 | 0.0404 | 79.70 | 130.1 | 158.2 | 0.2413 |
| 32 | 0.00795 | 0.202 | 0.0320 | 63.21 | 164.1 | 199.5 | 0.1913 |
Basis: Values are for solid, bare (uncoated) annealed copper. Resistance is calculated at 10.371 Ω·cmil/ft at 20°C (100% IACS), corrected to 75°C using α = 0.00393/°C. Stranded constructions run roughly 2–5% higher resistance than solid of the same AWG because of lay length, and tinned copper adds a further increment. Weight is bare conductor only — it excludes insulation, shielding, and jacketing.
| Gauge (AWG) | NEC Table 310.16 (raceway or cable, 30°C ambient) | Single conductor in free air |
Power transmission (700 cmil/A) |
||
|---|---|---|---|---|---|
| 60°C | 75°C | 90°C | |||
| 4/0 | 195 | 230 | 260 | 380 | 302 |
| 3/0 | 165 | 200 | 225 | 328 | 239 |
| 2/0 | 145 | 175 | 195 | 283 | 190 |
| 1/0 | 125 | 150 | 170 | 245 | 150 |
| 1 | 110 | 130 | 145 | 211 | 119 |
| 2 | 95 | 115 | 130 | 181 | 94 |
| 3 | 85 | 100 | 115 | 158 | 75 |
| 4 | 70 | 85 | 95 | 135 | 60 |
| 5 | — | 118 | 47 | ||
| 6 | 55 | 65 | 75 | 101 | 37 |
| 7 | — | 89 | 30 | ||
| 8 | 40 | 50 | 55 | 73 | 24 |
| 9 | — | 64 | 19 | ||
| 10 | 30 | 35 | 40‡ | 55 | 15 |
| 11 | — | 47 | 12 | ||
| 12 | 20 | 25 | 30‡ | 41 | 9.3 |
| 13 | — | 35 | 7.4 | ||
| 14 | 15 | 20 | 25‡ | 32 | 5.9 |
| 15 | — | 28 | 4.7 | ||
| 16 | — | 22 | 3.7 | ||
| 17 | — | 19 | 2.9 | ||
| 18 | — | 16 | 2.3 | ||
| 19 | — | 14 | 1.8 | ||
| 20 | — | 11 | 1.5 | ||
| 21 | — | 9 | 1.2 | ||
| 22 | — | 7 | 0.92 | ||
| 23 | — | 4.7 | 0.729 | ||
| 24 | — | 3.5 | 0.577 | ||
| 25 | — | 2.7 | 0.457 | ||
| 26 | — | 2.2 | 0.361 | ||
| 27 | — | 1.7 | 0.288 | ||
| 28 | — | 1.4 | 0.226 | ||
| 29 | — | 1.2 | 0.182 | ||
| 30 | — | 0.86 | 0.142 | ||
| 31 | — | 0.7 | 0.113 | ||
| 32 | — | 0.53 | 0.091 | ||
How to read this table. There is no single "max current" for a wire gauge. The right number depends on what the conductor is doing and what code governs it.
- NEC Table 310.16 applies to building wiring: not more than three current-carrying conductors in a raceway or cable, 30°C ambient. Apply the code's ambient temperature correction and conductor bundling adjustment factors for any other condition. The column you may use is limited by the temperature rating of the terminations at both ends (NEC 110.14(C)) — most equipment is listed at 75°C, so the 90°C column is usually available only for derating calculations, not for final sizing.
- ‡ Small-conductor rule (NEC 240.4(D)). Regardless of the 90°C column, overcurrent protection is limited to 15 A for 14 AWG, 20 A for 12 AWG, and 30 A for 10 AWG copper, with limited exceptions.
- Single conductor in free air is a conservative reference for a lone conductor with unrestricted airflow — chassis and panel wiring. It does not apply to bundled conductors, conduit, or cable jackets.
- Power transmission (700 cmil/A) is a very conservative rule of thumb for long runs where voltage drop and heat accumulation govern rather than short-term temperature rise. It is the most restrictive of the three and is not an NEC value.
- Below 14 AWG, general-purpose branch-circuit ampacities are not tabulated in the same way. Class 2 and Class 3 circuits, control wiring, and signal cable fall under NEC Article 725 and the applicable product standard.
This chart is a general engineering reference. It is not a substitute for the National Electrical Code or for the judgment of a licensed electrician or engineer. Size conductors to the code edition adopted in your jurisdiction and to the specific insulation type, ambient temperature, bundling, run length, and termination ratings of your installation.
Is a higher or lower AWG number thicker?
Lower. AWG runs backwards — 10 AWG is thicker than 20 AWG. Every 6-gauge step roughly doubles or halves the diameter, and every 3-gauge step roughly doubles or halves the cross-sectional area.
How many amps can 12 AWG copper wire handle?
It depends on the rating basis, and any single number quoted without one is guesswork. Under NEC Table 310.16, 12 AWG copper is rated 20 A at 60°C, 25 A at 75°C and 30 A at 90°C — but NEC 240.4(D) limits the overcurrent device to 20 A regardless of the column. As a single conductor in free air the conservative reference is about 41 A. On a long run where voltage drop governs, the 700 circular mils per amp rule gives 9.3 A.
How do I convert AWG to millimetres?
d(mm) = 0.127 × 92(36 − n) / 39, where n is the gauge number. Use n = 0, −1, −2 and −3 for 1/0, 2/0, 3/0 and 4/0. The chart above gives the result for every common size.
What is a circular mil?
The area of a circle one mil (0.001 in) in diameter. For a solid round conductor, circular mils = (diameter in mils)2, which makes area arithmetic trivial. Above 4/0, conductors are sized in thousands of circular mils (kcmil) rather than gauge numbers.
Does stranded wire have the same resistance as solid?
No. A stranded conductor of the same nominal AWG runs roughly 2–5% higher resistance than solid, because the individual strands follow a helical path longer than the cable itself. Tinned copper adds a further increment over bare.
Frequently Asked Questions About Copper Wire Gauge
A lower AWG number means a thicker wire. 1/0 AWG is far thicker than 24 AWG. As the gauge number rises, the conductor gets smaller and its resistance increases.
Every AWG size maps to a fixed diameter. Read the millimeter value for any gauge straight from the MM column in the table above. For example, 12 AWG is 2.053 mm and 24 AWG is 0.511 mm.
24 AWG copper wire has a diameter of 0.0201 inches, or 0.511 mm, with a cross-sectional area of 0.205 mm².
The Max Current column is a general reference. Real ampacity depends on insulation type, ambient temperature, bundling, and length. Size conductors to the National Electrical Code and confirm with a licensed electrician for your specific installation.