Maximum number of THHN/THWN-2 conductors in Rigid Metal Conduit (RMC), 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 344.
| Trade size | 40% area (in²) | 14 | 12 | 10 | 8 | 6 | 4 | 2 | 1/0 | 2/0 | 4/0 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 0.125 | 12 | 9 | 5 | 3 | 1 | 1 | 1 | — | — | — |
| 3/4" | 0.220 | 22 | 16 | 10 | 6 | 4 | 2 | 1 | 1 | 1 | — |
| 1" | 0.355 | 36 | 26 | 16 | 9 | 7 | 4 | 3 | 1 | 1 | 1 |
| 1-1/4" | 0.610 | 62 | 45 | 28 | 16 | 12 | 7 | 5 | 3 | 2 | 1 |
| 1-1/2" | 0.829 | 85 | 62 | 39 | 22 | 16 | 10 | 7 | 4 | 3 | 1 |
| 2" | 1.363 | 140 | 102 | 64 | 37 | 26 | 16 | 11 | 7 | 6 | 4 |
| 2-1/2" | 1.946 | 200 | 146 | 92 | 53 | 38 | 23 | 16 | 10 | 8 | 6 |
| 3" | 3.000 | 309 | 225 | 142 | 81 | 59 | 36 | 25 | 16 | 13 | 9 |
| 3-1/2" | 4.004 | 412 | 301 | 189 | 109 | 78 | 48 | 34 | 21 | 18 | 12 |
| 4" | 5.153 | 531 | 387 | 244 | 140 | 101 | 62 | 44 | 27 | 23 | 15 |
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.
Heavy-wall threaded steel conduit — the thickest and strongest raceway in the NEC. Used for service masts, hazardous locations, and anywhere physical damage is likely.