Rigid Conduit Fill Chart (RMC & IMC)
Maximum conductors for Rigid Metal Conduit (RMC) and Intermediate Metal Conduit (IMC), NEC 2023 Chapter 9.
RMC (NEC Article 344) and IMC (Article 342) share interior dimensions close to each other but distinct from EMT. IMC has a slightly larger ID than RMC at the same trade size — important when an inspector cites you for the wrong table. Use the conduit-type dropdown below to switch, and the conduit fill calculator for mixed wire pulls.
| TRADE → WIRE ↓ | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" | 5" | 6" |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 12 | 22 | 36 | 62 | 85 | 140 | 200 | 309 | 412 | 531 | 833 | 1000 |
| 12 AWG | 9 | 16 | 26 | 45 | 62 | 102 | 146 | 225 | 301 | 387 | 607 | 876 |
| 10 AWG | 5 | 10 | 16 | 28 | 39 | 64 | 92 | 142 | 189 | 244 | 383 | 552 |
| 8 AWG | 3 | 6 | 9 | 16 | 22 | 37 | 53 | 81 | 109 | 140 | 220 | 318 |
| 6 AWG | 1 | 4 | 6 | 12 | 16 | 26 | 38 | 59 | 78 | 101 | 159 | 230 |
| 4 AWG | 1 | 2 | 4 | 7 | 10 | 16 | 23 | 36 | 48 | 62 | 98 | 141 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 14 | 20 | 30 | 41 | 52 | 83 | 119 |
| 2 AWG | 1 | 1 | 3 | 5 | 7 | 11 | 16 | 25 | 34 | 44 | 69 | 100 |
| 1 AWG | 1 | 1 | 1 | 3 | 5 | 8 | 12 | 19 | 25 | 32 | 51 | 74 |
| 1/0 | — | 1 | 1 | 3 | 4 | 7 | 10 | 16 | 21 | 27 | 43 | 62 |
| 2/0 | — | 1 | 1 | 2 | 3 | 6 | 8 | 13 | 18 | 23 | 36 | 52 |
| 3/0 | — | 1 | 1 | 1 | 3 | 5 | 7 | 11 | 14 | 19 | 30 | 43 |
| 4/0 | — | — | 1 | 1 | 1 | 4 | 6 | 9 | 12 | 15 | 24 | 36 |
| 250 | — | — | 1 | 1 | 1 | 3 | 4 | 7 | 10 | 12 | 20 | 29 |
| 300 | — | — | 1 | 1 | 1 | 2 | 4 | 6 | 8 | 11 | 17 | 25 |
| 350 | — | — | — | 1 | 1 | 2 | 3 | 5 | 7 | 9 | 15 | 22 |
| 400 | — | — | — | 1 | 1 | 1 | 3 | 5 | 6 | 8 | 13 | 19 |
| 500 | — | — | — | 1 | 1 | 1 | 2 | 4 | 5 | 7 | 11 | 16 |
| 600 | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 | 9 | 13 |
| 700 | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 | 8 | 11 |
| 750 | — | — | — | — | 1 | 1 | 1 | 2 | 3 | 4 | 7 | 11 |
| 800 | — | — | — | — | — | 1 | 1 | 2 | 3 | 4 | 7 | 10 |
| 900 | — | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 6 | 9 |
| 1000 | — | — | — | — | — | 1 | 1 | 1 | 2 | 3 | 5 | 8 |
RMC — Rigid Metal Conduit × THHN (90°C dry) · NEC 2023 Ch.9 Tables 4 & 5 · 40% (3+), 31% (2), 53% (1)
NOTES & CONTEXT
RMC vs IMC — when to use each
RMC is the heaviest steel raceway — thick-wall, threaded, suitable for hazardous (classified) locations, service entrances, and outdoor risers. IMC is lighter (about 1/3 less weight) and accepted in most of the same applications as RMC, with the same fittings.
At 2" trade size: RMC has 3.408 in² interior; IMC has 3.630 in². That's a 6.5% capacity advantage to IMC at the same trade size — meaningful when you're right at the fill limit.
Rigid conduit wire fill calculation notes
- Threaded couplings reduce the effective length but not the cross-section — fill rules are unaffected.
- For pulls longer than 100 ft or with more than 360° of bends, upsize the conduit one trade size for pulling ease (NEC informational note).
- Bonding bushings on metal conduit do not reduce inside area.
Common RMC and IMC conduit fill scenarios
- 800-amp service riser: 3 × 600 kcmil + 1 × 1/0 ground in 4" RMC.
- Hazardous location feeder (Class I Div 1): RMC required, sized per the full conduit fill chart above.
- Industrial machine drop, 4 × 6 AWG XHHW: Fits 1" IMC at 35% fill.