Wire gauge and ampacity calculator
The smallest AWG or kcmil conductor that carries a load after NEC ambient and conductor-count derating, with the full ampacity table for the chosen column.
- Allowable ampacity after correction
- 44 A
- Load as share of allowable
- 90.9 %
- Conductor area
- 8.366 mm²
- Ambient correction factor
- 0.88
- Adjustment for conductor count
- 1
| Size | Area (mm²) | Table (A) | Corrected (A) |
|---|---|---|---|
| 14 AWG | 2.081 | 20 | 17.6 |
| 12 AWG | 3.309 | 25 | 22 |
| 10 AWG | 5.261 | 35 | 30.8 |
| 8 AWG | 8.366 | 50 | 44 |
| 6 AWG | 13.3 | 65 | 57.2 |
| 4 AWG | 21.15 | 85 | 74.8 |
| 3 AWG | 26.67 | 100 | 88 |
| 2 AWG | 33.63 | 115 | 101 |
| 1 AWG | 42.41 | 130 | 114 |
| 1/0 AWG | 53.48 | 150 | 132 |
| 2/0 AWG | 67.43 | 175 | 154 |
| 3/0 AWG | 85.03 | 200 | 176 |
| 4/0 AWG | 107.2 | 230 | 202 |
| 250 kcmil | 126.7 | 255 | 224 |
| 300 kcmil | 152 | 285 | 251 |
| 350 kcmil | 177.3 | 310 | 273 |
| 400 kcmil | 202.7 | 335 | 295 |
| 500 kcmil | 253.4 | 380 | 334 |
| 600 kcmil | 304 | 420 | 370 |
| 700 kcmil | 354.7 | 460 | 405 |
| 750 kcmil | 380 | 475 | 418 |
| 800 kcmil | 405.4 | 490 | 431 |
| 900 kcmil | 456 | 520 | 458 |
| 1000 kcmil | 506.7 | 545 | 480 |
| 1250 kcmil | 633.4 | 590 | 519 |
| 1500 kcmil | 760.1 | 625 | 550 |
| 1750 kcmil | 886.7 | 650 | 572 |
| 2000 kcmil | 1013 | 665 | 585 |
How this is calculated
I_allowed = I_table × F_ambient × F_count
I_table NEC Table 310.16 (raceway, cable, earth) or 310.17 (single conductor, free air)
F_ambient NEC Table 310.15(B)(1)(1), 30 °C basis
F_count NEC Table 310.15(C)(1): 4 to 6 = 0.80, 7 to 9 = 0.70, 10 to 20 = 0.50,
21 to 30 = 0.45, 31 to 40 = 0.40, 41 and above = 0.35
Result smallest size with I_allowed ≥ load- Tables
- Table 310.16 covers up to three current-carrying conductors in raceway, cable or earth at 30 °C. Table 310.17 covers single insulated conductors in free air at 30 °C. Both run to 2000 kcmil, from 14 AWG for copper (18 AWG in the 90 °C column) and 12 AWG for aluminum.
- Ambient
- Bands are whole degrees; a fractional ambient uses the next band up. Where the table shows no factor (for example 60 °C wire above 55 °C ambient) the rating is not permitted.
- Small conductors
- NEC 240.4(D) limits the overcurrent device to 15 A on 14 AWG, 20 A on 12 AWG and 30 A on 10 AWG copper, and 15 A and 25 A on 12 and 10 AWG aluminum, whatever the table ampacity. 18 and 16 AWG copper are limited to 7 A and 10 A, with conditions on the load and the protective device.
- Not included
- The 125 % continuous-load factor, termination temperature limits (110.14(C)), rooftop adders and voltage drop. Chassis and aerospace bundle ratings (SAE AS50881) are not included: their published curves could not be verified to a primary source.
- NFPA 70, National Electrical Code: Tables 310.16, 310.17, 310.15(B)(1)(1), 310.15(C)(1)2023 edition
- NFPA 70 2026 cycle First Draft, Code-Making Panel 6 working draft (reproduces the 2023 Tables 310.16, 310.17, 310.15(B)(1)(1) and 310.15(C)(1))NFPA, January 2024
- NFPA 70, National Electrical Code, as published by Public.Resource.Org: 240.4(D) and 110.14(C), and Tables 310.15(B)(16) and (17) used as a cross-check2017 edition
- ASTM B258, Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical ConductorsB258-18, reapproved 2026
Questions
In copper at 30 °C with up to three current-carrying conductors, 10 AWG: Table 310.16 gives it 30 A in the 60 °C column and 35 A at 75 °C. NEC 240.4(D) allows a 30 A breaker on 10 AWG copper. In aluminum, 10 AWG is 30 A at 75 °C but 240.4(D) limits it to a 25 A device, so a 30 A circuit takes 8 AWG.
Only for derating. NEC 110.14(C) caps the ampacity at the lowest rated termination, and equipment rated 100 A or less, or marked for 14 to 1 AWG, is 60 °C unless listed otherwise. Start from the 90 °C value, apply the ambient and count factors, then check the result does not exceed the 60 or 75 °C table value for that size.
Table 310.15(B)(1)(1) multiplies a 75 °C conductor by 0.88 at 36 to 40 °C and by 0.75 at 46 to 50 °C. 8 AWG copper at 75 °C drops from 50 A to 44 A at 40 °C. 60 °C insulation is not permitted above 55 °C ambient.
Above three current-carrying conductors in one raceway or cable, Table 310.15(C)(1) cuts every conductor to 80 % (4 to 6), 70 % (7 to 9) or 50 % (10 to 20). Nine 12 AWG THHN conductors at 90 °C carry 30 × 0.70 = 21 A each.
Single conductors in free air use NEC Table 310.17, which this calculator includes. Bundled harness derating to SAE AS50881 is not included because its curves could not be verified here; for bundles inside equipment, 310.16 with the conductor-count adjustment is the conservative choice.