Conduit Fill Calculator
Calculate conduit fill percentage per NEC Chapter 9 Table 1. Select conduit and add cables to check compliance.
Internal area: 346.4 mm²
Conduit fill calculation determines what percentage of a conduit's internal cross-sectional area is occupied by cables. The National Electrical Code (NEC) Chapter 9, Table 1 sets maximum fill percentages to prevent overheating, allow heat dissipation, and leave room for pulling additional cables in future.
How to use this calculator:
- Select your conduit type (EMT, IMC, PVC, etc.) and trade size
- Add cables from the predefined AV cable types, or enter custom cable dimensions
- The fill bar shows whether your cable bundle meets NEC requirements
- Toggle between imperial and metric units as needed
Tip: Always use the cable's listed outer diameter (OD), not the conductor size. Account for all cables in the conduit — power, data, and signal. Aim for 30% fill even though 40% is the NEC maximum for 3+ cables, to leave room for future additions and easier pulling.
Fill Status
6.8% fill across 1 cables
1 cable: 53% max fill
2 cables: 31% max fill
3+ cables: 40% max fill
Based on NEC Chapter 9, Table 1
Jam ratio predicts cable jamming risk at conduit bends. A ratio between 2.8–3.2 means cables can wedge during pulling.
Most applicable to 3 cables of similar diameter. Shown here as a general reference for all configurations.
● < 2.5 — No risk
● 2.5–2.8 — Low risk
● 2.8–3.2 — Jam danger
● > 3.2 — No risk
Formula: 1.05 × (Conduit ID / Avg Cable OD)
Disclaimer
These tools are provided in beta and are subject to change. All calculations and results may contain errors and should be independently verified by a qualified professional before use in any design, installation, or safety-critical application. AV500 accepts no liability for decisions made based on these outputs.