Overview
The conduit fill calculator determines whether a set of conductors fits within a given conduit size per NEC Chapter 9, Table 1 fill limits. It handles mixed conductor sizes by summing individual cross-sectional areas from Table 5 and comparing against the conduit’s internal area from Table 4.
If the selected conduit is too small, the calculator recommends the next size up that meets the fill requirement.
Fill Limits
NEC Chapter 9, Table 1 specifies maximum fill percentages:
| Number of Conductors | Maximum Fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| 3 or more | 40% |
These limits prevent physical damage during wire pulling and allow adequate heat dissipation. Exceeding them makes the pull physically difficult or impossible and can damage conductor insulation.
Supported Conduit Types
- EMT (Electrical Metallic Tubing) — 1/2” through 4”
- PVC Schedule 40 — 1/2” through 6”
- PVC Schedule 80 — 1/2” through 6”
- RMC (Rigid Metal Conduit) — 1/2” through 6”
- IMC (Intermediate Metal Conduit) — 1/2” through 4”
- FMC (Flexible Metal Conduit) — 3/8” through 4”
- LFMC (Liquidtight Flexible Metal Conduit) — 3/8” through 4”
NEC References
- NEC Chapter 9, Table 1 — percent fill limits
- NEC Chapter 9, Table 4 — conduit internal area by type and trade size
- NEC Chapter 9, Table 5 — conductor cross-sectional area by insulation type
- NEC Chapter 9, Table 5A — compact conductor areas
- NEC Chapter 9, Table 8 — bare conductor areas
Try it yourself
Calculate voltage drop for single-phase and three-phase circuits per NEC 2026 standards.
Calculate residential service size per NEC 2026 optional method with demand factor breakdown.
Calculate wire size per NEC Table 310.16 with temperature and conduit fill derating.
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