Fill limits (NEC Chapter 9, Table 1)
| Conductors | Maximum fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| 3 or more | 40% |
| Nipple 24 in or shorter | 60% |
Two conductors get the lowest limit because two round wires can jam against each other at a bend.
How it's calculated
Conductor area = Σ (count × area from Table 5)
Fill % = conductor area ÷ conduit area (Table 4) × 100
Areas are for THHN/THWN-2, the most common building wire. Equipment grounding conductors count toward fill. Bare grounds use the smaller area from Table 8.
THHN area reference (in²)
| 14 | 12 | 10 | 8 | 6 | 4 | 2 | 1/0 |
|---|---|---|---|---|---|---|---|
| 0.0097 | 0.0133 | 0.0211 | 0.0366 | 0.0507 | 0.0824 | 0.1158 | 0.1855 |
Fill is not the only limit
A conduit that passes fill can still be hard to pull. Long runs, several bends (360° maximum between pull points) and large conductors benefit from a size larger than the minimum. More than three current-carrying conductors also triggers ampacity derating under 310.15(C)(1).
Frequently asked questions
- How many 12 AWG THHN fit in 3/4 inch EMT?
- 16. Each is 0.0133 in², and 40% of 3/4 in EMT's 0.533 in² is 0.213 in².
- Do I count the ground wire in conduit fill?
- Yes. Equipment grounding and bonding conductors count toward fill (Chapter 9, Note 3), but not toward the current-carrying count for derating.
- Can I use this for XHHW or other insulation?
- Not directly. XHHW, RHW and other types have different areas in Table 5. THHN is the smallest common type, so other insulation needs more room.
Quick answers
- How many 12 AWG THHN wires fit in EMT?
- How many 10 AWG THHN wires fit in EMT?
- How many 14 AWG THHN wires fit in EMT?
- How many 12 AWG THHN wires fit in PVC Schedule 40?
- How many 8 AWG THHN wires fit in EMT?
- How many 10 AWG THHN wires fit in PVC Schedule 40?
- How many 6 AWG THHN wires fit in EMT?
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.