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.
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 |
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 2023
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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