The short answer
12 AWG THHN/THWN-2 has a cross-section of 0.0133 in². At the 40% fill limit for three or more conductors, 3/4" PVC Schedule 40 holds 15 and 1" holds 25. The smallest PVC Schedule 40 that fits even one is 1/2".
Maximum 12 AWG THHN by trade size
| Trade size | Max conductors | With Note 7 rounding | Conduit area (in²) |
|---|---|---|---|
| 1/2" | 8 | same | 0.285 |
| 3/4" | 15 | same | 0.508 |
| 1" | 25 | same | 0.832 |
| 1-1/4" | 43 | same | 1.453 |
| 1-1/2" | 59 | same | 1.986 |
| 2" | 98 | 99 | 3.291 |
| 2-1/2" | 141 | same | 4.695 |
| 3" | 218 | same | 7.268 |
| 3-1/2" | 292 | 293 | 9.737 |
| 4" | 377 | same | 12.554 |
"With Note 7 rounding": NEC Chapter 9, Note 7 lets you round up to the next whole conductor when the calculation comes out to a decimal of 0.8 or more and all the conductors are the same size. Annex C tables include that rounding.
How it's calculated
Conduit areas come from NEC Chapter 9 Table 4 and THHN areas from Table 5. One conductor may fill 53% and two conductors 31%. Count equipment grounding conductors toward fill. Mixing sizes? Use the calculator above, which handles up to three sizes at once.
Passing fill doesn't mean the pull will be easy. On long runs or runs with several bends, go one trade size up. More than three current-carrying conductors in one raceway also requires ampacity derating under NEC 310.15(C)(1).
Other wire sizes in PVC Schedule 40
10 AWG · 14 AWG · 8 AWG · 6 AWG · 4 AWG · 2 AWG · 3 AWG · 1 AWG · 1/0 AWG · 2/0 AWG · 3/0 AWG · 4/0 AWG
Open the full conduit fill calculator with these numbers
Results are estimates for planning and education. Verify against the current code edition your jurisdiction has adopted, manufacturer data and a licensed professional before you build or install.