Conduit Fill Calculator (EMT, RMC, PVC)
Tell us the wires and the conduit type, and get the fill percentage against the NEC limit (53% for one wire, 31% for two, 40% for three or more) and the smallest conduit trade size that works.
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How fill is calculated
Add up the cross-sectional area of every conductor (NEC Chapter 9, Table 5, THHN/THWN-2) and divide by the internal area of the conduit (Table 4). The allowed fill is 53% for 1 wire, 31% for 2 wires and 40% for 3 or more (Chapter 9, Table 1). The calculator also lists the smallest trade size that stays within the limit.
Note: the 40% limit applies to nipples over 24 inches. Nipples 24 inches or shorter may be filled to 60% (Table 1, Note 4). Ground and bonding conductors count toward fill.
Worked example
Six 12 AWG THHN wires (0.0133 in² each, 0.0798 in² total) in 1/2 in. EMT (0.304 in² internal) fill 26.3%, under the 40% limit.
Frequently asked questions
Do I count the ground wire?
Yes. Equipment grounding and bonding conductors count toward conduit fill.
What about different wire types?
This tool uses THHN/THWN-2 dimensions. Other insulation types such as XHHW or THW have different areas listed in Chapter 9 Table 5.
Is there a limit for short nipples?
Yes. A nipple 24 inches or shorter can be filled to 60%.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.