Conduit Fill Calculator

Check conduit fill for THHN/THWN-2 conductors in EMT and PVC Schedule 40 using NEC Chapter 9 Tables 1, 4 and 5.

Conduit fill

22.5 %

  • Allowed fill (NEC Ch. 9 Table 1)40 %
  • ResultWithin the limit
  • Max. conductors of this size (40%)16
  • Conductor area total0.1197 in²

Estimates only. Round up when you order, and confirm structural details with your local building code.

How to use it

  1. Pick the conduit type and trade size.
  2. Pick the wire size.
  3. Enter the number of current-carrying and grounding conductors.

The formula

Fill % = total conductor area ÷ conduit internal area

Limits: 53% for 1 conductor, 31% for 2, 40% for 3 or more

Worked example

Conduit typeEMT
Trade size3/4 in
Wire size (THHN/THWN-2)12 AWG
Number of conductors9

Result

Conduit fill22.5 %
Allowed fill (NEC Ch. 9 Table 1)40 %
ResultWithin the limit
Max. conductors of this size (40%)16
Conductor area total0.1197 in²

Tips before you order

  • Mixed wire sizes: add each conductor's area separately.
  • Fill limits are separate from ampacity derating for more than three current-carrying conductors.

Questions

How many 12 AWG wires in ¾ in EMT?

Up to 16 THHN conductors by fill (40% of 0.533 in² ÷ 0.0133 in²).