Conduit BendingBy Blissom · Updated 2026-10-23
Short answer: add up the area of every conductor (NEC Chapter 9, Table 5) and compare it with 40% of the conduit's internal area (Table 4) for three or more wires. If it does not exceed that allowance, the conduit passes the Chapter 9 fill check. Ampacity, installation conditions, pulling and the adopted code still have to be checked separately.
The 40% rule
| Conductors | Maximum fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| 3 or more | 40% |
| Nipple 24" or shorter between boxes, cabinets or similar enclosures (Note 4) | 60% |
Quick table: maximum THHN in EMT
| Wire | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" |
|---|---|---|---|---|---|---|
| #14 THHN | 12 | 22 | 35 | 61 | 84 | 138 |
| #12 THHN | 9 | 16 | 26 | 45 | 61 | 101 |
| #10 THHN | 5 | 10 | 16 | 28 | 38 | 63 |
| #8 THHN | 3 | 6 | 9 | 16 | 22 | 36 |
| #6 THHN | 2 | 4 | 7 | 12 | 16 | 26 |
For PVC, rigid, other wire types and every size up to 4", see the full conduit fill chart.
How conduit fill is calculated
- Look up each conductor's area in Chapter 9, Table 5 (for example #12 THHN = 0.0133 in²).
- Add them up. Nine #12 THHN = 0.1197 in².
- Look up the conduit's internal area in Table 4 (1/2" EMT = 0.304 in²) and take the allowed percentage: 40% of 0.304 = 0.1216 in².
- Compare. 0.1197 ≤ 0.1216, so nine #12 THHN fit.
Note 7 rounding
When every conductor has the same total area including insulation, a result such as 8.8 wires may be rounded up to 9 (Chapter 9, Note 7). The calculator and the tables on this site apply that rule, so they match the NEC Annex C tables.
Things the fill percentage does not tell you
- Ampacity adjustment: more than three current-carrying conductors in a raceway generally need ampacity adjustment (310.15(C)(1)). Exceptions apply, including qualifying raceways 24" or shorter, and equipment grounding conductors count for fill but not as current-carrying.
- Jamming: three conductors in a conduit with an inside-diameter-to-conductor ratio between 2.8 and 3.2 can jam on a pull around bends.
- Pull tension: a run at 40% with several bends can still be a hard pull; the bends between pull points must not exceed 360° (NEC 2023 358.24(B) for EMT; the 2026 NEC adds 300.24 for runs that combine raceway types).
Sources: NEC 2023: Chapter 9, Tables 1, 4 and 5, Note 7, and Annex C; Conductor areas for THHN/THWN, XHHW and THW from Chapter 9, Table 5. Method.
Questions electricians ask
How many 12 AWG wires can go in 1/2 EMT?
Nine #12 THHN/THWN-2 conductors fit in 1/2" EMT at 40% fill, and six #12 XHHW. For THW the site follows the conservative published Annex C count, four; a direct calculation from the Table 5 THW dimension (0.0181 in²) would allow six. Check the conductor you actually have and the edition you work to.
How many 12 AWG wires can go in 3/4 EMT?
Sixteen #12 THHN conductors fit in 3/4" EMT. For #10 THHN it is 10 and for #14 THHN it is 22.
What is the 40% conduit fill rule?
NEC Chapter 9, Table 1 allows conductors to take up 40% of the conduit's internal area when there are three or more. One conductor may take 53% and two conductors 31%; a conduit or tubing nipple of 24" or less installed between boxes, cabinets or similar enclosures may be filled to 60% (Note 4); not every short piece of conduit qualifies.
Does the ground wire count toward conduit fill?
Yes. Equipment grounding and bonding conductors count toward conduit fill (Chapter 9, Note 3), using their actual area; a bare ground uses the bare conductor area from Table 8.
What is Note 7?
Chapter 9, Note 7 says that when all conductors have the same total cross-sectional area, including insulation, a calculated count ending in .8 or more may be rounded up to the next whole number. It does not apply to mixed conductor areas. That is why the published tables sometimes allow one more wire than straight division gives.
Fill and box fill next to your bends
- Conduit fill with mixed wires, offline
- NEC 314.16 box fill with every allowance listed
- The smallest trade size that works
- Next to the bending calculators, saved jobs and PDF bend sheets
Android only. There is no iPhone version yet; the free calculators on this site work on any phone.
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