The Conduit Fill Calculator checks whether your conductors fit inside a conduit per NEC Chapter 9. Pick the conduit type and trade size, list your THHN wires by size and quantity, and read the fill percentage and compliance.
Conduit Fill Calculator
Calculate conduit fill for EMT, PVC, IMC and RMC. Enter the trade size and your THHN conductors to get the fill percentage and whether the run is compliant.
Inputs
Result
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conduit fill
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status
About Conduit Fill Calculator
Features
- EMT, PVC-40, IMC, RMC
- Trade sizes 1/2 to 4
- THHN conductor areas
- 1/2/>2 wire fill rules
How to Use
- Pick conduit type and trade size.
- List conductors as AWG:quantity per line.
- Read the fill percent and pass/fail.
Examples
Example: 3/4 EMT with four 12 AWG THHN -> about 24% fill (well within the 40% limit, pass).
Benefits
- Pick the right conduit size
- Avoid overfill pulling failures
Frequently Asked Questions
What is conduit fill?
It is the percentage of a conduit interior occupied by the conductors. NEC Chapter 9 limits it so wires can be pulled without damage.
What fill percent is allowed?
One conductor: 53%. Two conductors: 31%. More than two: 40% of the conduit interior area.
Which conductors are used?
The tool uses approximate THHN insulated areas. Enter each size and quantity, for example 12:4 and 10:2.
Is my data saved?
No. All math runs in your browser.