Flexible metal conduit (FMC, Greenfield) fill chart
The most THHN wires of one size each Flex 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 3/8" | 0.116 | 0.046 | 4 | 3 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1/2" | 0.317 | 0.127 | 13 | 9 | 6 | 3 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
| 3/4" | 0.533 | 0.213 | 22 | 16 | 10 | 6 | 4 | 2 | 1 | 1 | 0 | 0 | 0 |
| 1" | 0.817 | 0.327 | 33 | 24 | 15 | 9 | 6 | 4 | 3 | 1 | 1 | 1 | 0 |
| 1-1/4" | 1.277 | 0.511 | 52 | 38 | 24 | 14 | 10 | 6 | 4 | 2 | 1 | 1 | 0 |
| 1-1/2" | 1.858 | 0.743 | 76 | 56 | 35 | 20 | 14 | 9 | 6 | 4 | 1 | 1 | 1 |
| 2" | 3.269 | 1.308 | 135 | 98 | 62 | 35 | 25 | 16 | 11 | 7 | 4 | 3 | 1 |
| 2-1/2" | 4.909 | 1.964 | 202 | 147 | 93 | 53 | 38 | 24 | 17 | 10 | 6 | 5 | 2 |
| 3" | 7.069 | 2.828 | 291 | 212 | 134 | 77 | 55 | 34 | 24 | 15 | 8 | 7 | 4 |
| 3-1/2" | 9.621 | 3.848 | 396 | 289 | 182 | 105 | 76 | 46 | 33 | 20 | 12 | 9 | 5 |
| 4" | 12.566 | 5.026 | 518 | 378 | 238 | 137 | 99 | 61 | 43 | 27 | 15 | 12 | 7 |
Areas in square inches, from Chapter 9, Table 4 (2023 NEC). THHN/THWN-2 areas from Table 5.
About Flex
Flex is supported every 4-1/2 ft and within 12 in of each box (348.30). Short whips to equipment have their own exceptions. See strap spacing and the fill rules.