Permitted fill
| One conductor | 53% |
|---|---|
| Two conductors | 31% |
| More than two conductors | 40% |
2023 NEC
Conduit Fill Capacity Tables
Permitted fill percentages, conduit internal areas for EMT, PVC Schedule 40, and RMC, and conductor cross-sectional areas by insulation type.
NEC 2023Every value in this table is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
Conduit internal area (in²)
| Trade size | EMT | PVC Sch 40 | RMC |
|---|---|---|---|
| 1/2" | 0.304 | 0.285 | 0.314 |
| 3/4" | 0.533 | 0.508 | 0.549 |
| 1" | 0.864 | 0.832 | 0.887 |
| 1-1/4" | 1.496 | 1.453 | 1.526 |
| 1-1/2" | 2.036 | 1.986 | 2.071 |
| 2" | 3.356 | 3.291 | 3.408 |
| 2-1/2" | 5.858 | 4.695 | 4.866 |
| 3" | 8.846 | 7.268 | 7.499 |
| 3-1/2" | 11.545 | 9.737 | 10.01 |
| 4" | 14.753 | 12.554 | 12.882 |
Conductor area (in²)
| Size | THHN / THWN-2 | XHHW-2 | THW |
|---|---|---|---|
| 14 AWG | 0.0097 | 0.0139 | 0.0209 |
| 12 AWG | 0.0133 | 0.0181 | 0.026 |
| 10 AWG | 0.0211 | 0.0243 | 0.0333 |
| 8 AWG | 0.0366 | 0.0437 | 0.0556 |
| 6 AWG | 0.0507 | 0.059 | 0.0726 |
| 4 AWG | 0.0824 | 0.0814 | 0.0973 |
| 3 AWG | 0.0973 | 0.0962 | 0.1134 |
| 2 AWG | 0.1158 | 0.1146 | 0.1333 |
| 1 AWG | 0.1562 | 0.1534 | 0.1901 |
| 1/0 AWG | 0.1855 | 0.1825 | 0.2223 |
| 2/0 AWG | 0.2223 | 0.219 | 0.2624 |
| 3/0 AWG | 0.2679 | 0.2642 | 0.3117 |
| 4/0 AWG | 0.3237 | 0.3197 | 0.3718 |
| 250 kcmil | 0.397 | 0.3904 | 0.4596 |
| 300 kcmil | 0.4608 | 0.4536 | 0.5281 |
| 350 kcmil | 0.5242 | 0.5166 | 0.5958 |
| 400 kcmil | 0.5863 | 0.5782 | 0.6619 |
| 500 kcmil | 0.7073 | 0.6984 | 0.7901 |
| 600 kcmil | 0.8676 | 0.8709 | 0.9729 |
| 700 kcmil | 0.9887 | 0.9923 | 1.101 |
| 750 kcmil | 1.0496 | 1.0532 | 1.1652 |
| 800 kcmil | 1.1085 | 1.1122 | 1.2272 |
| 900 kcmil | 1.2311 | 1.2351 | 1.3561 |
| 1000 kcmil | 1.3478 | 1.3519 | 1.4784 |
| 1250 kcmil | - | 1.718 | 1.8602 |
| 1500 kcmil | - | 2.0156 | 2.1695 |
| 1750 kcmil | - | 2.3127 | 2.4773 |
| 2000 kcmil | - | 2.6073 | 2.7818 |
Source: NFPA 70, National Electrical Code, Chapter 9, Table 1; NFPA 70, National Electrical Code, Chapter 9, Table 4; NFPA 70, National Electrical Code, Chapter 9, Table 5. Published by NFPA.NEC 2023Transcribed from the 2023 NEC (NFPA 70, 2023). Confirm against your locally adopted edition and your authority having jurisdiction (AHJ).
Why two conductors get a lower limit than three
It looks like a typo but it isn't. Exactly two conductors in a round pipe can wedge against the wall on a bend - the jam ratio problem - while three or more bundle together and roll through. The tighter limit for two is a mechanical allowance, not a thermal one.
Fill and derating are the same problem
Both exist because bundled conductors cannot shed heat. Filling a conduit to the limit with current-carrying conductors will also trigger the bundling adjustment, reducing what each one carries. Passing the fill check does not mean the ampacity is unaffected.
Build a specific set in the conduit fill calculator, which handles mixed conductor sizes.
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