Intermediate metal conduit fill chart
The most THHN wires of one size each IMC size may hold, with three or more wires at 40 % fill. Pick a size for XHHW-2 and THW as well.
| Trade size | Inside area | 40 % | #14 | #12 | #10 | #8 | #6 | #4 | #2 | #1/0 | #4/0 | 250 kcmil | 500 kcmil |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 0.342 | 0.137 | 14 | 10 | 6 | 3 | 2 | 1 | 1 | 0 | 0 | 0 | 0 |
| 3/4" | 0.586 | 0.234 | 24 | 17 | 11 | 6 | 4 | 3 | 1 | 1 | 0 | 0 | 0 |
| 1" | 0.959 | 0.384 | 39 | 29 | 18 | 10 | 7 | 4 | 3 | 1 | 1 | 1 | 0 |
| 1-1/4" | 1.647 | 0.659 | 68 | 49 | 31 | 18 | 13 | 8 | 5 | 3 | 1 | 1 | 1 |
| 1-1/2" | 2.225 | 0.890 | 91 | 67 | 42 | 24 | 17 | 11 | 7 | 4 | 2 | 1 | 1 |
| 2" | 3.630 | 1.452 | 149 | 109 | 69 | 39 | 28 | 17 | 12 | 8 | 4 | 3 | 1 |
| 2-1/2" | 5.135 | 2.054 | 211 | 154 | 97 | 56 | 40 | 25 | 17 | 11 | 6 | 5 | 3 |
| 3" | 7.922 | 3.169 | 326 | 238 | 150 | 86 | 62 | 38 | 27 | 17 | 9 | 8 | 4 |
| 3-1/2" | 10.584 | 4.234 | 436 | 318 | 200 | 115 | 83 | 51 | 36 | 23 | 13 | 10 | 6 |
| 4" | 13.631 | 5.452 | 562 | 410 | 258 | 149 | 107 | 66 | 47 | 29 | 17 | 13 | 7 |
Areas in square inches, from Chapter 9, Table 4 (2023 NEC). THHN/THWN-2 areas from Table 5.
About IMC
IMC has a thinner wall than rigid, so it has a little more room inside size for size. Support follows 342.30: within 3 ft of each box, then every 10 ft, or longer on straight runs with threaded couplings. See strap spacing and the fill rules.