AWG Wire Gauge Chart — Diameter, Resistance & NEC Ampacity
AWG 14 to 500 kcmil conductor sizes with diameter, circular-mil area, and 75 °C copper resistance per NEC Chapter 9 Table 8, plus NEC 310.16 ampacities.
Updated August 16, 2026
American Wire Gauge runs backwards: smaller numbers are bigger wires, and above 4/0 AWG sizes switch to thousands of circular mils (kcmil). A circular mil is the area of a 0.001 in diameter circle, so the cmil column is exactly the squared diameter of an equivalent solid conductor in mils — which is why 250 kcmil means 250,000 cmil by definition. Every three gauge steps halves the resistance; every ten steps changes the area by a factor of ten.
The first table gives the physical constants for stranded, uncoated copper from NEC Chapter 9, Table 8 — the values used for voltage-drop and fault calculations. The second table is NEC Table 310.16: allowable ampacity for not more than three current-carrying conductors in raceway, cable, or earth at 30 °C ambient. It is rendered directly from the same data our conductor ampacity calculator uses, so the chart and the calculator always agree.
Remember that 310.16 is a starting point, not a final answer: ambient temperatures other than 30 °C, more than three current-carrying conductors, continuous loads (125%), and termination temperature limits all modify the usable value. The ampacity calculator applies those corrections in the code-prescribed order.
Conductor Properties (NEC Chapter 9, Table 8 — Stranded Copper)
| Size | Area (cmil) | Area (mm²) | Ø stranded (in) | Ø stranded (mm) | DC resistance, Cu 75 °C (Ω/1000 ft) |
|---|---|---|---|---|---|
| 14 AWG | 4,110 | 2.08 | 0.073 | 1.85 | 3.14 |
| 12 AWG | 6,530 | 3.31 | 0.092 | 2.32 | 1.98 |
| 10 AWG | 10,380 | 5.261 | 0.116 | 2.95 | 1.24 |
| 8 AWG | 16,510 | 8.367 | 0.146 | 3.71 | 0.778 |
| 6 AWG | 26,240 | 13.30 | 0.184 | 4.67 | 0.491 |
| 4 AWG | 41,740 | 21.15 | 0.232 | 5.89 | 0.308 |
| 3 AWG | 52,620 | 26.67 | 0.260 | 6.60 | 0.245 |
| 2 AWG | 66,360 | 33.62 | 0.292 | 7.42 | 0.194 |
| 1 AWG | 83,690 | 42.41 | 0.332 | 8.43 | 0.154 |
| 1/0 AWG | 105,600 | 53.49 | 0.372 | 9.45 | 0.122 |
| 2/0 AWG | 133,100 | 67.43 | 0.418 | 10.62 | 0.0967 |
| 3/0 AWG | 167,800 | 85.01 | 0.470 | 11.94 | 0.0766 |
| 4/0 AWG | 211,600 | 107.2 | 0.528 | 13.41 | 0.0608 |
| 250 kcmil | 250,000 | 127 | 0.575 | 14.61 | 0.0515 |
| 300 kcmil | 300,000 | 152 | 0.630 | 16.00 | 0.0429 |
| 350 kcmil | 350,000 | 177 | 0.681 | 17.30 | 0.0367 |
| 400 kcmil | 400,000 | 203 | 0.728 | 18.49 | 0.0321 |
| 500 kcmil | 500,000 | 253 | 0.813 | 20.65 | 0.0258 |
Class B stranded, uncoated copper. DC resistance at 75 °C per NEC Chapter 9, Table 8; kcmil areas in cmil are definitional (1 kcmil = 1,000 cmil). Solid conductors of the same size have slightly smaller diameters and marginally lower resistance.
Allowable Ampacity (NEC Table 310.16, 30 °C Ambient)
| Size | Cu 60 °C (A) | Cu 75 °C (A) | Cu 90 °C (A) | Al 60 °C (A) | Al 75 °C (A) | Al 90 °C (A) |
|---|---|---|---|---|---|---|
| 14 AWG | 15 | 20 | 25 | — | — | — |
| 12 AWG | 20 | 25 | 30 | 15 | 20 | 25 |
| 10 AWG | 30 | 35 | 40 | 25 | 30 | 35 |
| 8 AWG | 40 | 50 | 55 | 35 | 40 | 45 |
| 6 AWG | 55 | 65 | 75 | 40 | 50 | 55 |
| 4 AWG | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 AWG | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 AWG | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 AWG | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 AWG | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 AWG | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 AWG | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 AWG | 195 | 230 | 260 | 150 | 180 | 205 |
| 250 kcmil | 215 | 255 | 290 | 170 | 205 | 230 |
| 300 kcmil | 240 | 285 | 320 | 195 | 230 | 260 |
| 350 kcmil | 260 | 310 | 350 | 210 | 250 | 280 |
| 400 kcmil | 280 | 335 | 380 | 225 | 270 | 305 |
| 500 kcmil | 320 | 380 | 430 | 260 | 310 | 350 |
Not more than three current-carrying conductors in raceway, cable, or direct-buried, 30 °C (86 °F) ambient, per NEC 2023 Table 310.16. Aluminum is not produced in 14 AWG for this table. Apply ambient correction (310.15(B)(1)), bundling adjustment (310.15(C)(1)), the 125% continuous-load factor, and termination limits (110.14(C)) before selecting a conductor.
Sources & Further Reading
- NEC (NFPA 70) 2023, Chapter 9, Table 8 — Conductor Properties
- NEC (NFPA 70) 2023, Table 310.16 — Allowable Ampacities (as encoded and verified in the conductor ampacity calculator)
Frequently Asked Questions
Which ampacity column am I allowed to use?
The column matching your conductor insulation rating (e.g. THHN is 90 °C), but the final value can never exceed what the termination temperature allows — most breakers and lugs are rated 75 °C, and circuits 100 A and under often default to 60 °C terminations per NEC 110.14(C). The 90 °C column is mostly useful as the starting point for derating.
Why does 12 AWG copper show 30 A but get breakered at 20 A?
NEC 240.4(D) caps the overcurrent protection for 14, 12, and 10 AWG copper at 15, 20, and 30 A respectively regardless of the table value. The higher table numbers still matter: derating for ambient or bundling starts from the insulation-rated column, and the small-conductor cap is applied at the end.
How much does resistance change with temperature?
Copper resistance rises about 0.39% per °C. Table 8 lists DC resistance at 75 °C; at 20 °C the same conductor is roughly 18% lower. For AC circuits 250 kcmil and larger, skin effect adds measurably — NEC Chapter 9 Table 9 lists effective AC resistance for those cases.
What is a circular mil and why does the code use it?
One circular mil is the area of a circle 0.001 in across, so area in cmil equals the mil diameter squared — no π needed. It makes wire math convenient: the classic K-factor voltage-drop formula (K ≈ 12.9 Ω·cmil/ft for copper at 75 °C) divides directly by the cmil area from this chart.
Try the Calculators
AWG Wire Gauge Chart — Diameter, Resistance & NEC Ampacity — reuven.tools/reference/wire-gauge-ampacity — verified against: NEC (NFPA 70) 2023, Chapter 9, Table 8 — Conductor Properties; NEC (NFPA 70) 2023, Table 310.16 — Allowable Ampacities (as encoded and verified in the conductor ampacity calculator)