Conduit Fill Calculator
Calculate maximum wire capacity for electrical conduit
About this calculator
The Conduit Fill Calculator determines the maximum number of wires that can safely fit inside electrical conduit while meeting National Electrical Code (NEC) requirements. This tool helps electricians and contractors ensure proper wire capacity, prevent overheating, and maintain code compliance. By calculating the correct fill percentage, you can avoid costly rewiring, ensure electrical safety, and plan installations efficiently for residential, commercial, and industrial projects.
How to use
Select your conduit type and size from the dropdown menu, then choose the wire gauge and insulation type you plan to install. Enter the number of wires you want to run through the conduit. The calculator will instantly show whether your configuration meets NEC fill requirements and display the maximum allowable wire count.
Frequently asked questions
What is the NEC conduit fill rule?
The NEC limits conduit fill to 40% for three or more conductors to prevent overheating and allow for wire pulling without damage.
Can I mix different wire sizes in one conduit?
Yes, you can mix wire sizes, but the total cross-sectional area of all wires cannot exceed the conduit's fill capacity.
Do ground wires count toward conduit fill?
Yes, equipment grounding conductors count toward the total fill calculation and must be included in your wire count calculations.