IMC Conduit Fill Chart
Intermediate metal conduit wire capacity, computed from NEC 2023 Chapter 9 Tables 1, 4 and 5.
This is the complete IMC wire fill chart, computed live from NEC 2023 Chapter 9 Tables 4 and 5. Pick an insulation, filter by wire size, then export as CSV or print. For mixed conductor sizes in one run, use the interactive conduit fill calculator.
- 1/2" IMC10 wires
- 3/4" IMC17 wires
- 1" IMC29 wires
- 1-1/4" IMC49 wires
- 1-1/2" IMC67 wires
- 2" IMC109 wires
- 2-1/2" IMC154 wires
- 3" IMC238 wires
- 3-1/2" IMC318 wires
- 4" IMC410 wires
| TRADE → WIRE ↓ | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 14 | 24 | 39 | 68 | 91 | 149 | 211 | 326 | 436 | 562 |
| 12 AWG | 10 | 17 | 29 | 49 | 67 | 109 | 154 | 238 | 318 | 410 |
| 10 AWG | 6 | 11 | 18 | 31 | 42 | 69 | 97 | 150 | 200 | 258 |
| 8 AWG | 3 | 6 | 10 | 18 | 24 | 39 | 56 | 86 | 115 | 149 |
| 6 AWG | 2 | 4 | 7 | 13 | 17 | 28 | 40 | 62 | 83 | 107 |
| 4 AWG | — | 3 | 4 | 8 | 11 | 17 | 25 | 38 | 51 | 66 |
| 3 AWG | — | 2 | 4 | 6 | 9 | 15 | 21 | 32 | 43 | 56 |
| 2 AWG | 1 | — | 3 | 5 | 7 | 12 | 17 | 27 | 36 | 47 |
| 1 AWG | 1 | — | 2 | 4 | 5 | 9 | 13 | 20 | 27 | 35 |
| 1/0 | 1 | 1 | — | 3 | 4 | 8 | 11 | 17 | 23 | 29 |
| 2/0 | 1 | 1 | — | 3 | 4 | 6 | 9 | 14 | 19 | 24 |
| 3/0 | — | 1 | — | 2 | 3 | 5 | 7 | 12 | 16 | 20 |
| 4/0 | — | 1 | 1 | — | 2 | 4 | 6 | 9 | 13 | 17 |
| 250 | — | — | 1 | — | — | 3 | 5 | 8 | 10 | 13 |
| 300 | — | — | 1 | — | — | 3 | 4 | 7 | 9 | 12 |
| 350 | — | — | 1 | 1 | — | 2 | 4 | 6 | 8 | 10 |
| 400 | — | — | 1 | 1 | — | 2 | 3 | 5 | 7 | 9 |
| 500 | — | — | — | 1 | 1 | — | 3 | 4 | 6 | 7 |
| 600 | — | — | — | 1 | 1 | — | 2 | 3 | 5 | 6 |
| 700 | — | — | — | 1 | 1 | — | — | 3 | 4 | 5 |
| 750 | — | — | — | 1 | 1 | — | — | 3 | 4 | 5 |
| 800 | — | — | — | — | 1 | 1 | — | 3 | 4 | 5 |
| 900 | — | — | — | — | 1 | 1 | — | 2 | 3 | 4 |
| 1000 | — | — | — | — | 1 | 1 | — | 2 | 3 | 4 |
IMC — Intermediate Metal Conduit × THHN (90°C dry) · NEC 2023 Ch.9 Tables 4 & 5 · 40% (3+), 31% (2), 53% (1)
NOTES & CONTEXT
How to use the IMC fill chart
Each row is a trade size of intermediate metal conduit. The interior cross-sectional area comes straight from NEC 2023 Chapter 9 Table 4, and each conductor's area comes from Table 5. NEC Chapter 9 Table 1 sets the fill percentage you are allowed to occupy: 53 % for a single conductor, 31 % for exactly two conductors, and 40 % for three or more. A nipple no longer than 24 in may use 60 %. The chart applies the 40 % column by default because that is the most common install case.
What is IMC?
IMC is threadable rigid steel conduit governed by NEC Article 342. It uses a thinner wall than rigid metal conduit (RMC, Article 344) but is manufactured to the same outside diameter, so it is lighter to handle and cheaper by weight while remaining a true rigid raceway. NEC 342.10 permits IMC in every location where RMC is allowed, including direct burial, wet locations, and areas of physical damage.
Why IMC holds more wire than RMC or EMT
Because the wall is thinner but the outside diameter is fixed, IMC has a slightly larger interior than RMC at the same trade size, and a larger interior than EMT. A 1 in raceway is a clean example: 1 in IMC has 0.959 in² of interior area versus 0.887 in² for 1 in RMC and 0.864 in² for 1 in EMT. That extra area translates directly into conductor count, so an IMC run can sometimes carry the same conductors one trade size smaller than RMC. Compare the full tables on the RMC (rigid) conduit fill chart.
Common IMC scenarios
- Exposed feeder risers on a commercial exterior wall where a rigid steel raceway is required but weight matters.
- Service-entrance conduit from the meter to the panel, run in 1-1/4 in or 1-1/2 in IMC.
- Branch-circuit homeruns across a parking structure deck, where physical protection is needed and RMC would be heavier than necessary.
- Stub-ups feeding rooftop mechanical equipment, threaded into weatherproof fittings.
Reading the fill limits
The three fill percentages in NEC Chapter 9 Table 1 are not arbitrary. The 53 % single-conductor allowance leaves room for the conductor to be pulled and for the raceway to breathe; the 31 % two-conductor case is the strictest because two round conductors pack inefficiently and tend to bind; and the 40 % rule for three or more reflects the statistical packing of a bundle. IMC threading also matters here: because the raceway is threaded at each coupling, the pull is long and continuous, so staying at or under 40 % keeps pulling tension reasonable and protects the conductor jacket. When in doubt, size up one trade size rather than crowd a run at exactly the limit.
Grounding in IMC
IMC is a metallic raceway, so per NEC 250.118 the conduit itself can serve as the equipment grounding path when it is properly threaded and made up wrench-tight. Many designers still pull a separate equipment grounding conductor for reliability, and that conductor counts toward fill just like any other. Include it in your count before you compare against the chart, because forgetting the ground wire is the most common reason a run that looked legal turns out to be over the 40 % limit.
Heat de-rating note
This chart answers a geometry question only: how many conductors physically fit inside the conduit under NEC Chapter 9. It is not an ampacity table. Once more than three current-carrying conductors share a raceway, NEC 310.15(C)(1) requires adjustment of each conductor's allowable ampacity: 80 % for 4 to 6 current-carrying conductors, 70 % for 7 to 9, and 50 % for 10 to 20. A conduit that is legal on fill can still overheat if the ampacity adjustment is skipped, so size conductors for both fill and de-rated ampacity. Run your specific mix through the conduit fill calculator before ordering material.