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.
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.
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)