Calculate conduit fill percentage for EMT, PVC, RMC, IMC, FMC, and LFMC. Supports THHN, THWN, THWN-2, XHHW, RHW, and bare conductors with instant NEC compliance check.
Based on NEC Chapter 9 Tables 1, 4, and 5
All calculations provided by SparkShift are for reference and estimation purposes only. Results must be verified by a licensed Professional Engineer (PE), licensed electrician, or qualified person before use in any installation, design, or permit application.
Using NEC 2023 Chapter 9, Tables 1, 4, and 5
Click a preset to auto-fill, or configure manually below
NEC 358
The NEC limits conduit fill to prevent overheating and allow proper heat dissipation. Fill percentage = total conductor area ÷ conduit internal area.
| Conductors | Max Fill | Reference |
|---|---|---|
| 1 conductor | 53% | NEC Ch. 9 Table 1 |
| 2 conductors | 31% | NEC Ch. 9 Table 1 |
| 3+ conductors | 40% | NEC Ch. 9 Table 1 |
3/4" EMT = 0.533 in² x 40% = 0.213 in² available. Each #12 THHN = 0.0133 in². Result: 16 wires max.
Aim for 35% fill for easier pulls
Required for most commercial installs
360° max between pull points
IMPORTANT LEGAL DISCLAIMER
For Reference Only: This calculator is provided for educational and informational purposes only. It is not intended to be a substitute for professional engineering design, advice, or certification.
Code Compliance: Calculations are based on the 2023 National Electrical Code (NEC®). However, local codes, amendments, and Authority Having Jurisdiction (AHJ) requirements vary by location and may supersede standard NEC requirements.
Verify with Your AHJ: Local Authority Having Jurisdiction (AHJ) requirements take precedence over all general code references. Contact your local building department or electrical inspector to confirm applicable codes, amendments, and permit requirements before beginning any electrical work.
No Liability: SparkShift, LLC and its affiliates assume no liability for errors, omissions, or the use/misuse of this tool. Users are solely responsible for verifying all results against applicable codes and standards before installation. Always consult a licensed electrician or Professional Engineer (PE).
NEC Reference: NEC Chapter 9 Tables 1, 4, and 5
© 2026 SparkShift, LLC. Calculations are for reference only.
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