What is the NEC conduit fill limit?

NEC Chapter 9 allows 53% fill for one conductor, 31% for two conductors, and 40% for three or more conductors.

How do I calculate conduit fill?

Divide total wire cross-sectional area (sum of all conductor areas) by the internal area of the conduit, then multiply by 100 for percentage. Use NEC Chapter 9 Tables 4 and 5 for exact values.

What conduit size do I need for 4 wires?

Use the conduit fill calculator to find the minimum size. For example, four 12 AWG THHN wires (0.0133 sq in each = 0.053 sq in total) require at least 1/2" EMT (0.304 sq in × 40% = 0.122 sq in max).

Does ground wire count in conduit fill?

Yes, equipment grounding conductors count toward conduit fill calculations per NEC Chapter 9.

What is the difference between EMT, PVC, and RMC conduit?

EMT (thin-wall) is the most common for indoor wiring. PVC is used outdoors and underground. RMC (rigid metal conduit) is the heaviest and used for the most demanding applications.

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