NEC Conduit Fill Table

Maximum conductor counts from National Electrical Code (NEC) 2020 Annex C, tabulated by conduit type and wire type. Select conduit and wire — the table renders the pre-computed Annex C values for that combination. For mixed wire sizes or types, use the Conduit Fill Calculator instead.

How to use this table

  1. Select the conduit type — EMT, IMC, RMC, PVC Schedule 40, or PVC Schedule 80.
  2. Select the wire type — THHN/THWN/THWN-2 or XHHW/XHHW-2.
  3. Find the AWG or kcmil row and read the count at the desired trade size column.
  4. A cell showing — means that conductor does not fit at the applicable fill limit in that trade size.
  5. Use the Print button for a clean copy to keep in the truck or job folder.

NEC reference

Values are drawn from NEC 2020 Annex C, which pre-computes maximum conductor counts at the fill percentages in Chapter 9, Table 1: 53% for one conductor, 31% for two, and 40% for three or more. Conduit types correspond to Annex C tables as follows: EMT → Table C.1, IMC → Table C.4, RMC → Table C.8, PVC Schedule 80 → Table C.9, PVC Schedule 40 → Table C.10. These values are unchanged between NEC 2020 and NEC 2023 for the wire types listed — verify before use with any other edition.

Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.

When to use Annex C vs. calculating from scratch

Annex C exists to save the area math. It pre-computes the maximum number of identical conductors that fit in each conduit and trade size at the Chapter 9, Table 1 limits, so for a raceway carrying all one size and one insulation type, this table is the fastest correct answer. It applies only when every conductor is the same size and type. The moment you mix sizes — a run of #10 THHN with a #12 equipment grounding conductor, say — Annex C no longer applies, and you compute fill from conductor areas in NEC Chapter 9, Table 5 against the conduit area in Table 4.

Why counts differ by conduit type

Counts vary by conduit because internal cross-sectional area varies by wall construction. EMT is thin-wall; IMC and RMC are rigid threaded types with heavier walls. At the same trade size the internal areas in NEC Chapter 9, Table 4 differ, and IMC's larger internal area lets it hold equal or more conductors than EMT in several cells. PVC Schedule 80 has the thickest wall, so the smallest internal area and the lowest counts; PVC Schedule 40 sits between. Don't assume a count carries across conduit types — read the column for the raceway you're actually installing.

The 53 / 31 / 40 fill limits

Every Annex C count traces back to three limits in NEC Chapter 9, Table 1: a single conductor may fill 53% of the conduit's internal area, two conductors 31%, and three or more 40%. The two-conductor 31% case is the one that trips people up — it is more restrictive than the 40% applied at three and above, a deliberate jam-ratio allowance for pulling two conductors. Annex C bakes these percentages in, so each cell already reflects the correct limit for the quantity it represents.

Common mistakes

  • Applying the 53% figure to a multi-conductor run. 53% is the single-conductor limit. Three or more conductors are held to 40%, and two to 31%.
  • Forgetting the equipment grounding conductor. The EGC counts toward fill per NEC Chapter 9, Note 3 — including bare ones, sized by their Table 8 cross-section.
  • Treating Annex C as valid for mixed sizes. It is identical-conductor only. Mix sizes or insulation types and you must compute from Tables 4, 5, and 8.
  • Reading the wrong insulation column. THHN and XHHW-2 have different outside diameters; using the THHN count for XHHW-2 overfills the raceway, especially at small conductor sizes.

Frequently asked questions

How many conductors fit in 1-inch EMT?

It depends on conductor size and insulation. For #12 THHN, NEC Annex C Table C.1 allows 26 in 1-inch EMT; #10 THHN drops to 16, and #8 to 9. The table above lists every AWG and kcmil size for each trade size. These counts assume all conductors are the same size and type — the only case Annex C covers. Mixed sizes or types require an area calculation from Chapter 9, Tables 4 and 5.

Did conduit fill change between NEC 2020 and NEC 2023?

No, not for the common wire types. Conductor outside diameters in Chapter 9, Table 5 and conduit internal areas in Table 4 are unchanged for THHN, THWN-2, and XHHW-2 between the 2020 and 2023 editions, so the Annex C counts match. The fill percentages in Chapter 9, Table 1 — 53/31/40 — are also unchanged. On the 2017 edition or with a less common insulation, verify against that edition before relying on these counts.

THHN vs XHHW — which fits more in a conduit?

THHN/THWN-2 fits more than XHHW-2 at smaller sizes because XHHW-2 has thicker insulation and a larger outside diameter there. In 1/2-inch EMT you get 9 #12 THHN but 6 #12 XHHW. The gap narrows as conductor size increases and the two converge in the large kcmil range. Match the table column to the insulation actually printed on the conductor — substituting one for the other can overfill the raceway.

Does the equipment grounding conductor count toward conduit fill?

Yes. NEC Chapter 9, Note 3 requires equipment grounding and bonding conductors to be included in fill calculations, whether insulated or bare. For a bare EGC, use its actual cross-sectional area from Chapter 9, Table 8. Annex C assumes every conductor is the same size and type, so once you add an EGC of a different size, drop the table and compute fill from conductor areas.

How do I calculate conduit fill for mixed wire sizes?

Annex C only covers conduits filled with identical conductors. For mixed sizes or insulation types, sum each conductor area from Chapter 9, Table 5 (insulated) or Table 8 (bare), then compare the total to the allowable fill — 53% for one conductor, 31% for two, 40% for three or more — of the conduit internal area from Table 4. The Conduit Fill Calculator does this directly.

Related calculators