FIG. 01 — DIRECT ANSWER
How Many #12 THHN Fit in 1" PVC-40?
Maximum #12 THHN conductor count for 1" PVC-40 at the NEC 2023 40% fill cap (3 or more conductors).
FIG. 02
THE MATH IN ONE PASS
CONDUIT
1" PVC-40 (Article 352)
A = 0.8320 in²
NEC Ch.9 Table 4 — 100% interior area
40% allowable = 0.3328 in²
CONDUCTOR
#12 THHN
A₁ = 0.0133 in²
NEC Ch.9 Table 5 — single-conductor cross-section
0.3328 ÷ 0.0133 = 25 max
FIG. 03
STEP UP OR STEP DOWN A SIZE
| Trade size | Area (in²) | 40% allowed (in²) | Max #12 THHN |
|---|---|---|---|
| 3/4" PVC-40 (smaller) | 0.5080 | 0.2032 | 15 |
| 1" PVC-40 ← | 0.8320 | 0.3328 | 25 |
| 1-1/4" PVC-40 (larger) | 1.4530 | 0.5812 | 43 |
All values per NEC 2023 · Chapter 9 · Tables 1, 4 and 5. THHN/THWN-2/XHHW share identical conductor area.
FIG. 04
FREQUENTLY ASKED QUESTIONS
25 conductors, applying the NEC 2023 40% fill rule for 3+ conductors. The conduit's interior area is 0.8320 in² and the allowable conductor area is 0.3328 in² (NEC Ch.9 Table 4, Article 352).