Conduit Fill Calculator – Easy NEC-Compliant Wiring
When you are living in your home, commercial buildings, industrial projects then running wires through a conduit is quite common. But if you overfill a conduit, it will causr overheating, damaged wires or code violations. If you think you can guess this limit, it is quite risky. We have Conduit Fill Calculator which will make this process simple and easy.
⚡ Conduit Fill Calculator
Calculate conduit fill percentage based on conduit and wire specs.
How the Calculator Works
The tool considers:
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Conduit type: PVC, EMT, Rigid Steel, Flexible Metal
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Conduit size: ½”–4”
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Wire type: THHN, XHHW, TW
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Wire gauge & number of wires
It calculates the total wire area, compares it to NEC fill limits, and tells you whether your setup is safe. It also suggests a bigger conduit if needed.
NEC Conduit Fill Rules
| Number of Wires | Max Fill (%) |
|---|---|
| 1 | 53 |
| 2 | 31 |
| 3+ | 40 |
Different insulation types affect wire diameter:
| Wire Type | Typical Use | 14 AWG Diameter |
|---|---|---|
| THHN | Dry indoor | 0.111 in |
| XHHW | Moist/wet | 0.118 in |
| TW | Outdoor | 0.123 in |
How to Use this Calculator
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Select conduit type and size.
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Choose wire type and gauge.
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Enter the number of conductors.
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Click Calculate → see if the setup is safe or overfilled.
Example: 10 THHN wires, 12 AWG, in ¾” EMT conduit → safe. 20 wires → overfill warning.
FAQs
Q: Does every wire count toward fill?
Yes, Every wire count toward the fill which is including ground wires.
Q: Can I exceed limits for short runs?
No, NEC fill percentages apply to all conduit runs.
Q: Will overfilling affect wire performance?
Yes, Overfillinng can cause overheating and reduce safety.
