🔧 Calculate Conduit Fill
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👆 Add wires and click "Calculate Fill" to see results
Calculate conduit fill capacity based on NEC 2024 standards. Free, accurate, and easy to use.
👆 Add wires and click "Calculate Fill" to see results
Conduit fill refers to the percentage of a conduit's cross-sectional area occupied by wires and cables. The National Electrical Code (NEC) establishes maximum fill percentages to ensure proper heat dissipation and ease of wire installation.
According to NEC Article 314.16 and Chapter 9 Table 1:
Proper conduit fill prevents overheating, makes installation easier, reduces wire damage risk, and ensures compliance with electrical codes. Overfilled conduits can lead to installation difficulties and potential safety hazards.
Lightweight, easy to bend, most common for indoor applications. Not suitable for concrete burial.
Best for: Indoor commercial and residentialCorrosion-resistant plastic conduit. Schedule 80 has thicker walls for higher impact resistance.
Best for: Underground, corrosive environmentsHeavy-duty steel conduit with excellent protection. Can be threaded and buried directly.
Best for: Outdoor, industrial, high-protection areasLighter than RMC but stronger than EMT. Good balance of protection and weight.
Best for: Outdoor, commercial applicationsFlexible steel conduit for areas requiring movement or complex routing.
Best for: Motor connections, tight spacesWaterproof flexible conduit with plastic coating. Ideal for wet locations.
Best for: Outdoor equipment, wet locations| Wire Type | Temperature Rating | Insulation | Common Uses |
|---|---|---|---|
| THHN/THWN | 90°C (194°F) | Thermoplastic, nylon-coated | Most common for general purpose wiring |
| THWN-2 | 90°C (194°F) | Moisture and heat resistant | Wet and dry locations |
| XHHW/XHHW-2 | 90°C (194°F) | Cross-linked polyethylene | Industrial, high-temperature applications |
| RHH/RHW | 90°C (194°F) | Heat and moisture resistant rubber | Wet locations, underground |
| USE-2 | 90°C (194°F) | Underground service entrance | Direct burial, solar installations |
| TW | 60°C (140°F) | Thermoplastic, moisture resistant | General purpose, older installations |
When calculations show you're near the limit, consider using the next larger conduit size for easier installation and future expansion.
Don't forget to include ground wires, neutrals, and any control wires in your calculations.
While NEC provides baseline standards, local jurisdictions may have additional requirements.
Leave extra capacity for potential circuit additions or upgrades down the line.
More than 3 current-carrying conductors requires ampacity derating per NEC 310.15(C)(1).
Bundled conductors in long runs may require additional derating for heat dissipation.
Our conduit fill calculator helps electrical contractors, engineers, and DIY enthusiasts determine the correct conduit size for their wiring projects. Whether you're working with EMT conduit fill, PVC conduit sizing, or rigid metal conduit, this tool ensures NEC compliance.
Calculate wire fill percentage for various applications including residential conduit sizing, commercial electrical installations, and industrial power distribution. The calculator supports all common wire types including THHN, THWN, XHHW, and more.
Essential for determining maximum wire fill, conductor fill calculations, and ensuring proper electrical conduit sizing according to NEC Chapter 9 Table 1 requirements. Perfect for planning underground conduit runs, overhead conduit installations, and cable tray sizing.