4-inch Flexible Metal (FMC) Conduit Fill
Wire capacity of trade size 4 (metric designator 103) Flexible Metal Conduit (FMC), for THHN, XHHW, THW and RHW conductors from 14 AWG to 1000 kcmil.
4-inch Flexible Metal Conduit holds 99 × #6, 61 × #4, 43 × #2 or 27 × 1/0 AWG THHN conductors at 40% fill. Internal area: 12.566 in²; usable at 40%: 5.026 in².
| Wire size | THHN | XHHW | THW | RHW | THHN in a nipple (60%) | THHN area (in²) |
|---|---|---|---|---|---|---|
| 14 AWG | 518 | 361 | 361 | 171 | 777 | 0.0097 |
| 12 AWG | 378 | 277 | 277 | 142 | 567 | 0.0133 |
| 10 AWG | 238 | 207 | 207 | 115 | 357 | 0.0211 |
| 8 AWG | 137 | 115 | 115 | 60 | 206 | 0.0366 |
| 6 AWG | 99 | 85 | 69 | 48 | 148 | 0.0507 |
| 4 AWG | 61 | 61 | 51 | 37 | 91 | 0.0824 |
| 3 AWG | 51 | 52 | 44 | 33 | 77 | 0.0973 |
| 2 AWG | 43 | 44 | 37 | 28 | 65 | 0.1158 |
| 1 AWG | 32 | 32 | 26 | 19 | 48 | 0.1562 |
| 1/0 AWG | 27 | 27 | 22 | 16 | 40 | 0.1855 |
| 2/0 AWG | 22 | 23 | 19 | 14 | 34 | 0.2223 |
| 3/0 AWG | 18 | 19 | 16 | 12 | 28 | 0.2679 |
| 4/0 AWG | 15 | 15 | 13 | 10 | 23 | 0.3237 |
| 250 kcmil | 12 | 13 | 11 | 8 | 19 | 0.3970 |
| 300 kcmil | 11 | 11 | 9 | 7 | 16 | 0.4608 |
| 350 kcmil | 9 | 9 | 8 | 6 | 14 | 0.5242 |
| 400 kcmil | 8 | 8 | 7 | 6 | 13 | 0.5863 |
| 500 kcmil | 7 | 7 | 6 | 5 | 10 | 0.7073 |
| 600 kcmil | 5 | 5 | 5 | 4 | 8 | 0.8676 |
| 700 kcmil | 5 | 5 | 4 | 3 | 7 | 0.9887 |
| 750 kcmil | 4 | 4 | 4 | 3 | 7 | 1.0496 |
| 800 kcmil | 4 | 4 | 4 | 3 | 7 | 1.1085 |
| 900 kcmil | 4 | 4 | 3 | 3 | 6 | 1.2311 |
| 1000 kcmil | 3 | 3 | 3 | 3 | 5 | 1.3478 |
Mixed wire sizes? Calculate it
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4-inch conduit: Flexible Metal Conduit vs other types
Trade size is nominal. The real inside diameter, and so the wire count, changes with the wall thickness of each raceway type.
| Conduit type | ID (in) | Area (in²) | 40% (in²) | #12 THHN | #10 THHN | #6 THHN |
|---|---|---|---|---|---|---|
| EMT | 4.334 | 14.753 | 5.901 | 443 | 279 | 116 |
| PVC Schedule 40 | 3.998 | 12.554 | 5.022 | 377 | 238 | 99 |
| PVC Schedule 80 | 3.786 | 11.258 | 4.503 | 338 | 213 | 89 |
| Rigid Metal Conduit | 4.050 | 12.882 | 5.153 | 387 | 244 | 101 |
| IMC | 4.166 | 13.631 | 5.452 | 410 | 258 | 107 |
| Flexible Metal Conduit | 4.000 | 12.566 | 5.026 | 378 | 238 | 99 |
| Liquidtight Flexible Metal Conduit | 4.020 | 12.692 | 5.077 | 381 | 240 | 100 |
Other Flexible Metal Conduit sizes
Frequently asked questions
How many #12 wires fit in 4-inch Flexible Metal Conduit?
378 conductors of 12 AWG THHN/THWN-2 at the 40% fill limit. With thicker THW or XHHW insulation the count is 277.
What is the inside diameter and area of 4-inch Flexible Metal Conduit?
The internal diameter is 4.000 in. (101.6 mm) and the total cross-sectional area is 12.566 in². The usable area is 5.026 in² at 40% fill, 3.895 in² for two wires and 6.660 in² for one.
What is the largest wire I can pull three of in 4-inch Flexible Metal Conduit?
1000 kcmil THHN: 3 conductors fit at 40% fill. That is three current-carrying conductors with no ground; add the ground’s area and check again with the calculator if you need one.
Can I really load it with that many conductors?
For space, yes. But 378 current-carrying conductors in one raceway means heavy ampacity derating — 10 to 20 conductors are adjusted to 50% of their table ampacity. Fill tells you what fits; derating tells you what it can carry.
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