Conduit Fill Calculator (NEC)
Select the raceway, trade size, conductor insulation, wire size, and count for an instant NEC Chapter 9 fill check.
Formula and worked example
Frequently asked questions
What is the NEC conduit fill rule?
NEC Chapter 9 Table 1 permits 53% fill for one conductor, 31% for two conductors, and 40% for three or more conductors.
What is the fill for three #12 THHN wires in 3/4-inch EMT?
Three #12 THHN conductors occupy 7.49% of 3/4-inch EMT, below the 40% limit.
Does insulation type change conduit fill?
Yes. Chapter 9 Table 5 conductor areas vary by insulation type, so THHN, XHHW, and RHH of the same wire size may produce different fill.
Are equipment grounding conductors counted for conduit fill?
Yes. Every insulated or bare conductor in the raceway occupies area and must be included in the conduit-fill calculation.
Related
NEC calculations in your pocket.
Nine electrical calculators that follow the NEC. Ohm's law, power/kVA, wire sizing, voltage drop, conduit fill (mixed conductors), motor FLA + OCPD, box fill, service load, reference. Free on the App Store and Google Play.
