Maximum number of THHN/THWN-2 conductors in Intermediate Metal Conduit (IMC), trade sizes 1/2 inch through 4 inch. Internal areas from NEC Chapter 9, Table 4; fill limits from Table 1 (53% for one conductor, 31% for two, 40% for three or more). NEC Article 342.
| Trade size | 40% area (in²) | 14 | 12 | 10 | 8 | 6 | 4 | 2 | 1/0 | 2/0 | 4/0 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 0.137 | 14 | 10 | 6 | 3 | 2 | 1 | 1 | — | — | — |
| 3/4" | 0.235 | 24 | 17 | 11 | 6 | 4 | 2 | 1 | 1 | 1 | — |
| 1" | 0.384 | 39 | 28 | 18 | 10 | 7 | 4 | 3 | 1 | 1 | 1 |
| 1-1/4" | 0.659 | 67 | 49 | 31 | 18 | 12 | 7 | 5 | 3 | 2 | 1 |
| 1-1/2" | 0.890 | 91 | 66 | 42 | 24 | 17 | 10 | 7 | 4 | 4 | 2 |
| 2" | 1.452 | 149 | 109 | 68 | 39 | 28 | 17 | 12 | 7 | 6 | 4 |
| 2-1/2" | 2.054 | 211 | 154 | 97 | 56 | 40 | 24 | 17 | 11 | 9 | 6 |
| 3" | 3.169 | 326 | 238 | 150 | 86 | 62 | 38 | 27 | 17 | 14 | 9 |
| 3-1/2" | 4.234 | 436 | 318 | 200 | 115 | 83 | 51 | 36 | 22 | 19 | 13 |
| 4" | 5.452 | 562 | 409 | 258 | 148 | 107 | 66 | 47 | 29 | 24 | 16 |
Column headings are AWG conductor sizes, all THHN/THWN-2. A dash means the conductor does not fit even as a single conductor at the 53% limit.
Threaded steel conduit with a thinner wall than RMC, so it is lighter and has slightly more internal area. Permitted anywhere RMC is permitted.