FREE ELECTRICAL CALCULATOR
Conduit Fill Calculator
Check conduit fill percentage and the approximate maximum number of matching conductors for common raceways and THHN/THWN-2 sizes.
How the conduit-fill calculation works
The calculator divides the total listed conductor area by the conduit’s internal area. It applies the general Chapter 9 Table 1 limits of 53% for one conductor, 31% for two conductors, and 40% for more than two conductors.
Important checks before installation
- Confirm the exact conductor insulation type and dimensions.
- Apply ampacity adjustment and temperature correction separately.
- Count equipment grounding conductors when determining raceway fill.
- Verify the conduit type, trade size, conductor listing, and current adopted code.
Planning aid only. Verify calculations against the currently adopted NEC, manufacturer listings, and local requirements.