Conduit Fill Calculator

This calculator helps determine the appropriate conduit size based on the number and type of cables you need to run. Fill limits follow National Electrical Code (NEC) Chapter 9, Table 1: 53% of the conduit's internal cross-sectional area for a single cable, 31% for two cables, and 40% for three or more. Conduit internal diameters are for EMT per NEC Chapter 9, Table 4.

• Cable Areas: The calculator uses the Outer Diameter (OD) of each cable type to calculate its circular area (Area = π * (OD/2)²). The total area for each cable type is its area multiplied by the quantity.
• Total Cable Area: All individual cable areas are summed up to get a grand total area for all cables.
• Conduit Sizing: The calculator then checks standard EMT trade sizes. It finds the smallest conduit where the total cable area is within the applicable NEC fill limit.
• Alternative Sizing: An alternative calculation is provided for scenarios where a maximum conduit size (e.g., 1-1/4") is preferred. Cables are packed individually across multiple conduits (largest first), so no single cable is ever split across conduits, and each conduit respects the fill limit for its own cable count. The last conduit is downsized where possible.

The reference tables for conduit sizes and cable characteristics provide the underlying data used in these calculations. You can also add custom cables if your specific type isn't listed.