Rigid metal conduit (RMC, GRC) fill chart
The most THHN wires of one size each Rigid 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" | 0.314 | 0.126 | 13 | 9 | 6 | 3 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
| 3/4" | 0.549 | 0.220 | 22 | 16 | 10 | 6 | 4 | 2 | 1 | 1 | 0 | 0 | 0 |
| 1" | 0.887 | 0.355 | 36 | 26 | 17 | 9 | 7 | 4 | 3 | 1 | 1 | 1 | 0 |
| 1-1/4" | 1.526 | 0.610 | 63 | 46 | 29 | 16 | 12 | 7 | 5 | 3 | 1 | 1 | 1 |
| 1-1/2" | 2.071 | 0.828 | 85 | 62 | 39 | 22 | 16 | 10 | 7 | 4 | 1 | 1 | 1 |
| 2" | 3.408 | 1.363 | 140 | 102 | 64 | 37 | 27 | 16 | 11 | 7 | 4 | 3 | 1 |
| 2-1/2" | 4.866 | 1.946 | 200 | 146 | 92 | 53 | 38 | 23 | 17 | 10 | 6 | 5 | 2 |
| 3" | 7.499 | 3.000 | 309 | 225 | 142 | 82 | 59 | 36 | 26 | 16 | 9 | 7 | 4 |
| 3-1/2" | 10.010 | 4.004 | 412 | 301 | 189 | 109 | 79 | 48 | 34 | 21 | 12 | 10 | 5 |
| 4" | 12.882 | 5.153 | 531 | 387 | 244 | 140 | 101 | 62 | 44 | 27 | 16 | 13 | 7 |
| 5" | 20.212 | 8.085 | 833 | 608 | 383 | 221 | 159 | 98 | 70 | 43 | 25 | 20 | 11 |
| 6" | 29.158 | 11.663 | 1202 | 877 | 552 | 318 | 230 | 141 | 100 | 63 | 36 | 29 | 16 |
Areas in square inches, from Chapter 9, Table 4 (2023 NEC). THHN/THWN-2 areas from Table 5.
About Rigid
Rigid (galvanized rigid conduit, GRC) has the thickest wall and the least room inside of the steel types. Support follows 344.30: within 3 ft of each box, then every 10 ft, or longer on straight runs with threaded couplings (Table 344.30(B)(2)). See strap spacing and the fill rules.