Conduit Fill by Wire Count

Fill percentage and maximum conductor count for EMT and PVC 40 by trade size and wire gauge, with the 53, 31, and 40 percent rules and the 24 in nipple exception.

Grounding conductors and the equipment ground count against fill. Three or more conductors is the 40 percent rule; two is 31 percent; one is 53 percent; a 24 in nipple gets 60 percent.

—Fill used by your conductors
—Code limit that applies to you
—Pass / fail on this conduit size
—Max conductors of this gauge in this size
—Next trade size that passes
—60 percent nipple count (24 in) at spares
How the math works
  • Fill percentages (NEC Chapter 9, Table 1): one conductor 53%, two conductors 31%, three or more 40%. A 24 in nipple (a length of raceway 24 in or less) gets 60% under Chapter 9, Note 4.
  • Conduit areas (Chapter 9, Table 4): EMT: 1/2 = 0.304, 3/4 = 0.533, 1 = 0.864, 1¼ = 1.496, 1½ = 2.137, 2 = 3.031, 3 = 6.321, 4 = 11.461 sq in. PVC 40 runs smaller: 1/2 = 0.264, 3/4 = 0.454, 1 = 0.750, 2 = 2.530.
  • Conductor areas (Chapter 9, Table 1): THHN/THWN-2: 14 = 0.00973, 12 = 0.01330, 10 = 0.02116, 8 = 0.03629, 6 = 0.05067, 4 = 0.08155, 1/0 = 0.2297, 4/0 = 0.4781. XHHW-2 runs bigger: 12 = 0.01780, 10 = 0.02660, 6 = 0.06360.
  • What counts: every current-carrying conductor plus the neutral plus the equipment grounding conductor. A 3-wire 240 V circuit with a neutral and a ground is 5 conductors, and 16 of them in 3/4 in EMT is 12.5% over the 40% limit.
  • Derating: 4 to 6 current-carrying conductors derate ampacity to 80%, 7 to 9 to 50% (310.15(C)(1)). Fill capacity and ampacity are two different limits, and ampacity is the one that kills a fat conduit run.
Fill calculator for the common 600 V building wire types listed. Table 1 areas for the compact and expanded types differ, so match your wire to the right column: THWN (wet, non-compact) is larger than THWN-2, and XHHW-2 is larger than both. Multi-conductor cable, MC, and Type AC assemblies fill by their own Table 5/7 entries, and 40% fill in a 10 ft run with 360° bends is a pulling problem long before it is a code problem.

How many 12 gauge THHN wires fit in 3/4 inch EMT?

16 conductors at the 40% rule (0.213 sq in allowed / 0.0133 = 16.0). One conductor gets 53% (21 wires), two get 31% (12), and 17 wires is over the limit.

How many 12-3 with ground in a 1 inch conduit?

A 12-3 with ground cable is not a raceway fill item, cables fill by Table 5 area of the assembly. For 12 AWG THHN individual conductors, 1 in EMT takes 26 conductors at 40% (0.346 / 0.0133). A 3-wire plus neutral plus ground run is 5 conductors, and 5 of them fit easily.

Is the 40 percent fill limit about heat?

No, it is about pulling the wire in: the areas model the heat rise from a bundle plus the practical pull. Ampacity derating is a separate rule (310.15(C)(1)) that bites at 4 conductors, so a conduit that passes fill at 9 wires has already lost 50% of its ampacity.

Related tools

Wire ampacity & breaker sizeDerating from conductor count Voltage drop & wire sizeBigger wire needs bigger conduit Service load calculatorFeeder and raceway sizing Wire pull box sizeThe box at the pull point