Gauge Charts
Wire Gauge Chart
American Wire Gauge runs backwards: the smaller the number, the thicker the wire. 4/0 is the largest size in common building work at 0.4600 inches, and each step up in gauge number is about 89 percent of the previous diameter, so six gauge numbers roughly halves the diameter and cuts the cross-sectional area by four.
AWG size chart
Diameters and areas are fixed by the AWG definition, a geometric series between 4/0 at 0.4600 inches and 36 AWG at 0.0050 inches. Resistance is NEC Chapter 9, Table 8 for uncoated copper at 75 degrees C.
| AWG | Diameter (in) | Diameter (mm) | Area (cmil) | Area (mm2) | Ohms/1000 ft |
|---|---|---|---|---|---|
| 24 | 0.0201 | 0.51 | 404 | 0.20 | 25.67 |
| 22 | 0.0253 | 0.64 | 640 | 0.32 | 16.14 |
| 20 | 0.0320 | 0.81 | 1,020 | 0.52 | 10.15 |
| 18 | 0.0403 | 1.02 | 1,620 | 0.82 | 7.95 |
| 16 | 0.0508 | 1.29 | 2,580 | 1.31 | 4.99 |
| 14 | 0.0641 | 1.63 | 4,110 | 2.08 | 3.14 |
| 12 | 0.0808 | 2.05 | 6,530 | 3.31 | 1.98 |
| 10 | 0.1019 | 2.59 | 10,380 | 5.26 | 1.24 |
| 8 | 0.1285 | 3.26 | 16,510 | 8.37 | 0.778 |
| 6 | 0.1620 | 4.11 | 26,240 | 13.30 | 0.491 |
| 4 | 0.2043 | 5.19 | 41,740 | 21.15 | 0.308 |
| 3 | 0.2294 | 5.83 | 52,620 | 26.70 | 0.245 |
| 2 | 0.2576 | 6.54 | 66,360 | 33.60 | 0.194 |
| 1 | 0.2893 | 7.35 | 83,690 | 42.40 | 0.154 |
| 1/0 | 0.3249 | 8.25 | 105,600 | 53.50 | 0.122 |
| 2/0 | 0.3648 | 9.27 | 133,100 | 67.40 | 0.0967 |
| 3/0 | 0.4096 | 10.40 | 167,800 | 85.00 | 0.0766 |
| 4/0 | 0.4600 | 11.68 | 211,600 | 107.20 | 0.0608 |
How the AWG numbers work
- The scale is geometric, not linear. Every gauge step multiplies the diameter by about 0.8905.
- Three gauge steps roughly halves the cross-sectional area. Six steps halves the diameter.
- Sizes above 1 AWG are written 1/0, 2/0, 3/0 and 4/0, spoken as "one aught" through "four aught". They keep getting thicker in that order.
- Past 4/0 the scale stops and conductors are specified in thousands of circular mils (kcmil) instead.
- Stranded and solid wire of the same AWG have the same cross-sectional area of copper, but stranded has a slightly larger overall diameter.
Wire terms, defined
Ampacity
- The maximum current a conductor can carry continuously without exceeding its temperature rating. It is a property of the conductor, its insulation and its surroundings, not of the circuit.
Circular mil
- The area of a circle one thousandth of an inch in diameter. Conductor area in circular mils is simply the diameter in mils squared, which is why the unit exists.
Aught
- The spoken form of the zero in sizes above 1 AWG. 1/0 is "one aught", 4/0 is "four aught", and each one is thicker than the last.
kcmil
- Thousands of circular mils. Conductors larger than 4/0 leave the AWG scale and are specified this way instead, starting at 250 kcmil.
Derating
- Reducing a conductor's table ampacity to account for high ambient temperature or for more than three current-carrying conductors sharing a raceway.
Common questions
Is a higher gauge number thicker or thinner wire?
- Thinner. The AWG scale runs backwards, so 20 AWG is thinner than 10 AWG. The numbering comes from the drawing process: a wire pulled through more successive dies gets a higher number and a smaller diameter.
How many amps can 12 gauge wire carry?
- NEC Table 310.16 lists 12 AWG copper at 20 A in the 60 degree C column, 25 A at 75 degrees C and 30 A at 90 degrees C. In practice NEC 240.4(D) caps the overcurrent protection for 12 AWG copper at 20 A regardless of insulation, so a 20 A breaker is the normal answer.
What is the difference between AWG and mm2?
- AWG is a gauge number on a fixed geometric scale; mm2 is the actual cross-sectional area. They are not interchangeable, and no AWG size lands exactly on a standard metric size. 12 AWG is 3.31 mm2, which sits between the 2.5 mm2 and 4 mm2 metric conductors.