Reference tables · Conduit fill
RMC (rigid metal conduit)
4" RMC has an internal area of 12.882 in². At the 40% limit that applies to more than two conductors, it holds up to 387 12 AWG THHN conductors, counted with the same-size rounding rule (Chapter 9, Note 7).
Capacity
NEC 2023Every count in this table is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
| Conductor | THHN / THWN-2 | XHHW-2 | THW |
|---|---|---|---|
| 14 AWG | 531 | 370 | 246 |
| 12 AWG | 387 | 284 | 198 |
| 10 AWG | 244 | 212 | 154 |
| 8 AWG | 140 | 118 | 92 |
| 6 AWG | 101 | 87 | 71 |
| 4 AWG | 62 | 63 | 53 |
| 3 AWG | 53 | 53 | 45 |
| 2 AWG | 44 | 45 | 38 |
| 1 AWG | 33 | 33 | 27 |
| 1/0 AWG | 27 | 28 | 23 |
| 2/0 AWG | 23 | 23 | 19 |
| 3/0 AWG | 19 | 19 | 16 |
| 4/0 AWG | 16 | 16 | 14 |
| 250 kcmil | 13 | 13 | 11 |
| 300 kcmil | 11 | 11 | 9 |
| 350 kcmil | 10 | 10 | 8 |
| 400 kcmil | 8 | 9 | 7 |
| 500 kcmil | 7 | 7 | 6 |
| 600 kcmil | 6 | 6 | 5 |
| 700 kcmil | 5 | 5 | 4 |
| 750 kcmil | 5 | 5 | 4 |
| 800 kcmil | 4 | 4 | 4 |
| 900 kcmil | 4 | 4 | 3 |
| 1000 kcmil | 4 | 4 | 3 |
| 1250 kcmil | - | 3 | 2 |
| 1500 kcmil | - | 2 | 2 |
| 1750 kcmil | - | 1 | 1 |
| 2000 kcmil | - | 1 | 1 |
How the counts are computed: the conduit area (Chapter 9, Table 4) at the permitted fill (53% for one conductor, 31% for two, 40% for more) divided by one conductor's area (Chapter 9, Table 5). A result whose decimal is 0.8 or more is taken as the next whole number, which Chapter 9, Note 7 allows only when every conductor is the same size. Mixed sizes never round up; use the conduit fill calculator for those.
Published tables differ for THW in 14 to 8 AWG. This site uses the larger area, which gives the lower count. Check your edition.
NEC 2023Every area and limit below is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.
| Internal area | 12.882 in² |
|---|---|
| One conductor | 53% - 6.8275 in² |
| Two conductors | 31% - 3.9934 in² |
| More than two | 40% - 5.1528 in² |
These counts are the mathematical fill limit, not a promise the pull will go well. A raceway at 39% fill with four 90° bends and a hundred feet between pull points is legal and miserable. Experienced installers routinely size up a trade size on long or bendy runs, and the material cost difference is usually smaller than the labour cost of a fight.
Two other things this table does not model. Nipples 24 inches and shorter between enclosures are permitted a much higher fill. And a mixed set of conductor sizes has to be summed by area rather than looked up by count - the conduit fill calculator handles that.
Remember also that conductor count drives ampacity derating separately. Filling this conduit with current-carrying conductors will reduce what each one can carry - see the bundling adjustment table.
Source: NFPA 70, National Electrical Code, Chapter 9, Table 1; NFPA 70, National Electrical Code, Chapter 9, Table 4; NFPA 70, National Electrical Code, Chapter 9, Table 5; NFPA 70, National Electrical Code, Chapter 9, Note 7. Published by NFPA.NEC 2023Transcribed from the 2023 NEC (NFPA 70, 2023). Confirm against your locally adopted edition and your authority having jurisdiction (AHJ).
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