Rigid Conduit Fill Chart (RMC & IMC)
Maximum conductor count for rigid metal conduit (RMC) and intermediate metal conduit (IMC), computed from published internal diameters and nominal THHN outside diameters.
Quick answer
1/2 inch RMC holds 9 12 AWG THHN conductors and 3/4 inch holds 16. IMC has a thinner wall and slightly more usable area, holding 10 and 17 in the same trade sizes. Fill limits are 40% for three or more conductors, 31% for two and 53% for one.
RMC (rigid metal conduit) — maximum THHN/THWN-2 conductors
Same-size conductors only. Mixed sizes need the conduit fill calculator.
| Wire size | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" |
|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG | 12 | 22 | 36 | 63 | 85 | 140 | 200 | 200 | 200 | 200 |
| 12 AWG | 9 | 16 | 26 | 45 | 62 | 102 | 146 | 200 | 200 | 200 |
| 10 AWG | 5 | 10 | 16 | 28 | 39 | 64 | 92 | 142 | 189 | 200 |
| 8 AWG | 3 | 5 | 9 | 16 | 22 | 37 | 53 | 81 | 109 | 140 |
| 6 AWG | 1 | 4 | 7 | 12 | 16 | 26 | 38 | 59 | 79 | 101 |
| 4 AWG | 1 | 2 | 4 | 7 | 10 | 16 | 23 | 36 | 48 | 62 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 14 | 19 | 30 | 41 | 52 |
| 2 AWG | 1 | 1 | 3 | 5 | 7 | 11 | 16 | 25 | 34 | 44 |
| 1 AWG | 1 | 1 | 1 | 3 | 5 | 8 | 12 | 19 | 25 | 32 |
| 1/0 AWG | — | 1 | 1 | 3 | 4 | 7 | 10 | 16 | 21 | 27 |
| 2/0 AWG | — | 1 | 1 | 2 | 3 | 6 | 8 | 13 | 18 | 23 |
| 3/0 AWG | — | 1 | 1 | 1 | 3 | 5 | 7 | 11 | 15 | 19 |
| 4/0 AWG | — | — | 1 | 1 | 1 | 4 | 6 | 9 | 12 | 15 |
Published standard — source: RMC (rigid metal conduit) internal diameters from the product standard; conductor OD from nominal THHN dimensions
IMC (intermediate metal conduit) — maximum THHN/THWN-2 conductors
Same-size conductors only. Mixed sizes need the conduit fill calculator.
| Wire size | 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 | 150 | 200 | 200 | 200 | 200 |
| 12 AWG | 10 | 17 | 28 | 49 | 67 | 109 | 154 | 200 | 200 | 200 |
| 10 AWG | 6 | 11 | 18 | 31 | 42 | 68 | 97 | 150 | 200 | 200 |
| 8 AWG | 3 | 6 | 10 | 17 | 24 | 39 | 56 | 86 | 115 | 148 |
| 6 AWG | 2 | 4 | 7 | 12 | 17 | 28 | 40 | 62 | 83 | 107 |
| 4 AWG | 1 | 2 | 4 | 7 | 10 | 17 | 24 | 38 | 51 | 66 |
| 3 AWG | 1 | 1 | 3 | 6 | 9 | 14 | 21 | 32 | 43 | 56 |
| 2 AWG | 1 | 1 | 3 | 5 | 7 | 12 | 17 | 27 | 36 | 47 |
| 1 AWG | 1 | 1 | 1 | 4 | 5 | 9 | 13 | 20 | 27 | 34 |
| 1/0 AWG | — | 1 | 1 | 3 | 4 | 7 | 11 | 17 | 22 | 29 |
| 2/0 AWG | — | 1 | 1 | 2 | 4 | 6 | 9 | 14 | 19 | 24 |
| 3/0 AWG | — | 1 | 1 | 1 | 3 | 5 | 7 | 11 | 15 | 20 |
| 4/0 AWG | — | — | 1 | 1 | 2 | 4 | 6 | 9 | 13 | 16 |
Published standard — source: IMC (intermediate metal conduit) internal diameters from the product standard; conductor OD from nominal THHN dimensions
Rigid conduit internal area by trade size
| Trade size | RMC area | IMC area |
|---|---|---|
| 1/2" | 0.314 (0.125) | 0.342 (0.137) |
| 3/4" | 0.549 (0.220) | 0.586 (0.235) |
| 1" | 0.887 (0.355) | 0.959 (0.384) |
| 1-1/4" | 1.526 (0.610) | 1.647 (0.659) |
| 1-1/2" | 2.071 (0.829) | 2.225 (0.890) |
| 2" | 3.408 (1.363) | 3.631 (1.452) |
| 2-1/2" | 4.866 (1.946) | 5.135 (2.054) |
| 3" | 7.499 (3.000) | 7.922 (3.169) |
| 3-1/2" | 10.010 (4.004) | 10.584 (4.234) |
| 4" | 12.883 (5.153) | 13.631 (5.452) |
Source & method: Area is A = π × (id / 2)². Internal diameters are nominal published product dimensions; see the methodology page.
Conductor outside diameters used
| Size | Insulated OD (in) | Area (sq in) |
|---|---|---|
| 18 AWG | 0.084 | 0.0055 |
| 16 AWG | 0.096 | 0.0072 |
| 14 AWG | 0.111 | 0.0097 |
| 12 AWG | 0.130 | 0.0133 |
| 10 AWG | 0.164 | 0.0211 |
| 8 AWG | 0.216 | 0.0366 |
| 6 AWG | 0.254 | 0.0507 |
| 4 AWG | 0.324 | 0.0824 |
| 3 AWG | 0.352 | 0.0973 |
| 2 AWG | 0.384 | 0.1158 |
| 1 AWG | 0.446 | 0.1562 |
| 1/0 AWG | 0.486 | 0.1855 |
| 2/0 AWG | 0.532 | 0.2223 |
| 3/0 AWG | 0.581 | 0.2651 |
| 4/0 AWG | 0.642 | 0.3237 |
| 250 kcmil | 0.711 | 0.3970 |
| 300 kcmil | 0.766 | 0.4608 |
| 350 kcmil | 0.817 | 0.5242 |
| 400 kcmil | 0.864 | 0.5863 |
| 500 kcmil | 0.949 | 0.7073 |
| 600 kcmil | 1.051 | 0.8676 |
| 750 kcmil | 1.158 | 1.0532 |
Frequently asked
- How many 12 AWG wires fit in 1/2 inch RMC?
- Using nominal THHN outside diameters and the 40% fill rule, 9 12 AWG conductors fit in 1/2 inch RMC. Every conductor counts, including the neutral and the equipment grounding conductor.
- What is the maximum fill percentage for rigid conduit?
- 40% of the internal cross-sectional area for three or more conductors, 31% for exactly two and 53% for a single conductor. Nipples 24 inches or shorter are permitted at 60%.
- What size rigid conduit do I need for three 10 AWG conductors?
- Three 10 AWG THHN conductors need at least 1/2 inch RMC at 40% fill. Add a fourth conductor and re-check, because the count changes the usable area.
- Does the ground wire count toward conduit fill?
- Yes. Fill counts every conductor in the raceway. Grounds are excluded only from the ampacity adjustment count for current-carrying conductors, never from fill.
- Where do these rigid conduit numbers come from?
- Internal diameters are published product dimensions from the relevant ANSI/UL/ASTM product standards. Area is computed as pi times radius squared, and the conductor count is the largest whole number that fits inside the applicable fill percentage. No code table is reproduced.
Mixed conductor sizes
These tables cover one conductor size at a time. Use the conduit fill calculator for mixed sizes, or see the full conduit fill chart for every raceway type side by side.
Raceway and pulling supplies
Raceway and pulling supplies
Common trade sizes and pulling gear.
- 3/4 in rigid conduit3/4 in rigidRaceway in the trade size this fill calculation used.Check price on Amazon →
- 3/4 in connectors & couplings3/4 inFittings sized to match the raceway run.Check price on Amazon →
- Wire pulling lubricantCuts pulling tension on long or high-fill runs.Check price on Amazon →
- Conduit bender3/4 inHand bender matched to this trade size.Check price on Amazon →
Links go to Amazon search results, not a single listing — confirm ratings, insulation type and listing details before buying, and make sure the part is approved for your application.
Related charts & calculators
- Voltage Drop CalculatorPercent drop, end voltage and minimum conductor for any run length.
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- Breaker Size CalculatorOvercurrent device rating and minimum conductor from load current.
- Wire Ampacity CalculatorDerated ampacity for ambient temperature and bundled conductors.
- Box Fill CalculatorVolume allowances for conductors, clamps, devices and grounds per NEC 314.16.
- Ampacity ChartEstimated allowable ampacity by conductor size, material and insulation rating.