Conduit Fill Calculator
Check NEC conduit fill compliance: calculate fill percentage, compare to code limits, and find maximum conductor count.
Inputs
mm
AWG
conductors
(1=THHN, 2=XHHW)
Results
Fill Percentage
9.1%
NEC Compliant?
1 (1=yes, 0=no)
Conduit Internal Area387 mm²
Area per Conductor11.68 mm²
Total Fill Area35.04 mm²
Max Conductors Allowed13 conductors
How to Use This Calculator
- Select the Conduit Trade Size in mm: 16 mm = 1/2", 21 mm = 3/4", 27 mm = 1", 35 mm = 1-1/4", 53 mm = 2".
- Enter the Conductor Size in AWG and the Conductor Type (THHN or XHHW) — conductor OD varies by insulation type.
- Enter the Number of Conductors to be pulled through the conduit.
- Review the Fill Percentage — NEC Chapter 9 allows 40% fill for 3+ conductors, 31% for 2, and 53% for 1 conductor.
- Check the NEC Compliant? output — a value of 1 means the fill is within limits; 0 means you must upsize the conduit.
- Note the Max Conductors Allowed to quickly assess how many more wires could be added to an existing conduit.
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