Conduit Fill Calculator

Check NEC conduit fill percentage for EMT, PVC and IMC — instant pass/fail result.

Total Fill Area
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sq in
Fill Percentage
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%
NEC Limit
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%
Max Conductors
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—

How the Conduit Fill Calculator Works

This calculator uses NEC Table 4 conduit internal areas and NEC Table 5 THHN/THWN wire cross-section areas to determine how much of a conduit's interior is occupied by conductors. Total fill area equals the wire's cross-section area multiplied by the number of conductors. That result is divided by the conduit's internal area and expressed as a percentage. The NEC (Article 300 and Chapter 9, Table 1) sets fill limits to prevent heat buildup and allow for future wire pulling: 53% for one conductor, 31% for two conductors, and 40% for three or more. The calculator also shows the maximum number of conductors of the selected gauge that would fit within the applicable NEC limit, so you can plan conduit sizing before installation.

Frequently Asked Questions

What is the NEC conduit fill limit?
The NEC allows 40% fill for 3 or more conductors, 31% for 2 conductors, and 53% for a single conductor (Table 1, Chapter 9).
How many #12 THHN wires fit in ½-inch EMT?
½-inch EMT has 0.304 sq in of area. At 40% fill (0.122 sq in), and #12 THHN at 0.0133 sq in each, you can fit 9 conductors.
What is the difference between EMT and PVC conduit?
EMT (Electrical Metallic Tubing) is thin-walled steel, used indoors and in dry locations. PVC is non-metallic, corrosion-resistant, and used outdoors or underground.
Can I mix wire gauges in one conduit?
Yes. Sum the cross-sectional areas of all conductors and compare to the conduit's allowable fill area. The NEC doesn't prohibit mixing sizes.

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