Conduit Wire Fill Calculator

NEC Annex C, Table C.1 permits up to 16 THHN 12 AWG conductors in 3/4-inch EMT. Annex C lists ready-made counts for same-size conductors of one insulation type, so it is the fastest way to answer 'how many wires fit' without summing areas by hand.

Yes. The equipment grounding conductor (EGC) occupies space in the raceway, so its cross-sectional area counts toward the fill total even though it is not a current-carrying conductor. Counting for ampacity derating is a separate rule and treats the ground differently.

Look up each conductor's cross-sectional area in NEC Chapter 9, Table 5, multiply by quantity, and sum all areas. Compare the total against the conduit's allowable fill area, which is the Table 4 interior area multiplied by the 40% limit for three or more conductors.

Annex C gives pre-calculated conductor counts for conduits filled with a single size and type of conductor. Chapter 9 Tables 4 and 5 give the raw conduit interior areas and conductor areas you use to calculate mixed-size fills manually. Use Annex C for same-size runs, the area method for mixed sizes.

Yes. PVC and EMT have different interior diameters at the same trade size, so their usable fill areas differ. A 1-inch PVC Schedule 40 conduit holds a different conductor count than 1-inch EMT, which is why the calculator asks for raceway type.

Total your conductor areas, then select the smallest trade size whose 40% fill area meets or exceeds that total. The calculator does this automatically and returns the minimum recommended conduit size for your conductor set.