1-inch IMC Conduit Fill
Wire capacity of trade size 1 (metric designator 27) Intermediate Metal Conduit, for THHN, XHHW, THW and RHW conductors from 14 AWG to 1000 kcmil.
1-inch IMC holds 39 × #14, 29 × #12, 18 × #10 or 10 × #8 THHN conductors at 40% fill. Internal area: 0.959 in²; usable at 40%: 0.384 in².
| Wire size | THHN | XHHW | THW | RHW | THHN in a nipple (60%) | THHN area (in²) |
|---|---|---|---|---|---|---|
| 14 AWG | 39 | 27 | 27 | 13 | 59 | 0.0097 |
| 12 AWG | 29 | 21 | 21 | 11 | 43 | 0.0133 |
| 10 AWG | 18 | 15 | 15 | 8 | 27 | 0.0211 |
| 8 AWG | 10 | 8 | 8 | 4 | 15 | 0.0366 |
| 6 AWG | 7 | 6 | 5 | 3 | 11 | 0.0507 |
| 4 AWG | 4 | 4 | 4 | 3 | 7 | 0.0824 |
| 3 AWG | 4 | 4 | 3 | 1 | 6 | 0.0973 |
| 2 AWG | 3 | 3 | 3 | 1 | 5 | 0.1158 |
| 1 AWG | 1 | 1 | 1 | 1 | 3 | 0.1562 |
| 1/0 AWG | 1 | 1 | 1 | 1 | 3 | 0.1855 |
| 2/0 AWG | 1 | 1 | 1 | 1 | 2 | 0.2223 |
| 3/0 AWG | 1 | 1 | 1 | 1 | 2 | 0.2679 |
| 4/0 AWG | 1 | 1 | 1 | 1 | 1 | 0.3237 |
| 250 kcmil | 1 | 1 | 1 | — | 1 | 0.3970 |
| 300 kcmil | 1 | 1 | — | — | 1 | 0.4608 |
| 350 kcmil | — | — | — | — | 1 | 0.5242 |
| 400 kcmil | — | — | — | — | 1 | 0.5863 |
| 500 kcmil | — | — | — | — | 1 | 0.7073 |
| 600 kcmil | — | — | — | — | — | 0.8676 |
| 700 kcmil | — | — | — | — | — | 0.9887 |
| 750 kcmil | — | — | — | — | — | 1.0496 |
| 800 kcmil | — | — | — | — | — | 1.1085 |
| 900 kcmil | — | — | — | — | — | 1.2311 |
| 1000 kcmil | — | — | — | — | — | 1.3478 |
Mixed wire sizes? Calculate it
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1-inch conduit: IMC 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 | 1.049 | 0.864 | 0.346 | 26 | 16 | 7 |
| PVC Schedule 40 | 1.029 | 0.832 | 0.333 | 25 | 15 | 6 |
| PVC Schedule 80 | 0.936 | 0.688 | 0.275 | 20 | 13 | 5 |
| Rigid Metal Conduit | 1.063 | 0.887 | 0.355 | 26 | 17 | 7 |
| IMC | 1.105 | 0.959 | 0.384 | 29 | 18 | 7 |
| Flexible Metal Conduit | 1.020 | 0.817 | 0.327 | 24 | 15 | 6 |
| Liquidtight Flexible Metal Conduit | 1.054 | 0.873 | 0.349 | 26 | 16 | 7 |
| ENT | 1.029 | 0.832 | 0.333 | 25 | 15 | 6 |
Other IMC sizes
Frequently asked questions
How many #12 wires fit in 1-inch IMC?
29 conductors of 12 AWG THHN/THWN-2 at the 40% fill limit. With thicker THW or XHHW insulation the count is 21.
What is the inside diameter and area of 1-inch IMC?
The internal diameter is 1.105 in. (28.1 mm) and the total cross-sectional area is 0.959 in². The usable area is 0.384 in² at 40% fill, 0.297 in² for two wires and 0.508 in² for one.
What is the largest wire I can pull three of in 1-inch IMC?
2 AWG 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 29 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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