Fill rules used
Standard calculations use NEC Chapter 9 Table 1 fill limits: 53% for one conductor or cable, 31% for two, and 40% for more than two. The optional nipple toggle applies the 60% fill allowance for nipples not over 24 inches.
Tool
Conduit fill calculator
NEC-based fill checks with cable data, sizing guidance, and a scaled conduit view.
Raceway setup
Pick the conduit and the rule set.
The calculator uses the selected raceway interior dimensions and the actual cable or conductor outside diameters entered below.
Conduit I.D. -
100% area -
Current rule -
Cable schedule
Add conductors or cables.
Use the library for known cable diameters or switch a row to custom when your project cable differs from the reference set.
Count each single conductor or each multiconductor cable as one item in the number field. For non-round cables, use the major outside dimension as your custom diameter input.
NEC notes
How this calculator applies the code logic.
Actual cable diameters
For cables not listed directly in NEC conductor tables, the tool uses actual outside diameters from manufacturer data or your custom entry, consistent with the NEC notes for mixed conductor and cable fill calculations.
Reference libraries
Each library item includes a reference part number and a cutsheet link where manufacturer documentation is available.