Calculate conduit fill percentages per CEC Table 8 and NEC. Enter your conductors and conduit size to check you are within code limits: 53% for one conductor, 31% for two, 40% for three or more.
Conduit fill is the percentage of a conduit’s internal cross-sectional area taken up by the conductors inside it. You total the area of every conductor, including insulation, and divide by the usable area of the conduit.
The maximum allowed percentage depends on how many conductors are in the raceway: 53 percent for a single conductor, 31 percent for exactly two, and 40 percent for three or more. The calculator handles CEC Table 8, NEC Chapter 9, LSZH conductors, and a custom fill percentage if your local code differs.
Say you are pulling three #10 RW90 copper conductors. You add up the total insulated area of the three conductors, then compare it against 40 percent of the internal area of the trade size you are considering. If the conductors exceed 40 percent of a 1/2 inch conduit, the calculator steps you up to 3/4 inch, where the fill lands comfortably under the limit.
The CEC governs conduit fill in Rule 12-910 and the tables in Section 12, with conductor and conduit dimensions in the Table 8 and Table 9 series and Table 6 for specific raceways. The NEC uses Chapter 9 Table 1 for the fill percentages and Table 4 and Table 5 for raceway and conductor areas. These are pointers only; verify dimensions against the current code edition and manufacturer data.
One conductor is 53 percent, two conductors is 31 percent, and three or more is 40 percent of the conduit internal cross-sectional area. This applies under both the CEC and NEC.
Yes. Every current-carrying and bonding conductor in the raceway counts toward the fill percentage, including the equipment grounding or bonding conductor.
The lower limit for exactly two conductors reflects how two round conductors pack inside a round raceway and leave less usable space than a single conductor or a larger bundle.
Yes. The calculator supports a custom fill percentage for local codes or internal standards that differ from the standard CEC and NEC limits.