How to Use the Electrical Conduit Size Calculator
Packing too many conductors into a conduit makes pulling wire difficult and traps heat, which can damage insulation over time. This calculator uses NEC Chapter 9 Table 5 conductor areas (THHN) and Table 4 conduit fill limits to recommend the minimum standard EMT trade size for your job.
Select the conductor AWG size and how many conductors will share the conduit. The tool applies the correct NEC fill limit automatically β 53% for a single conductor, 31% for two conductors, or 40% for three or more β then finds the smallest EMT trade size whose internal area satisfies that limit.
Real installations also depend on the number of bends, conductor type, and pull length, so treat this result as a planning estimate. Always confirm final conduit sizing with a licensed electrician against the current NEC edition and local code.
Frequently Asked Questions
Conduit fill is the percentage of a conduit's cross-sectional area occupied by conductors. NEC Chapter 9 Table 1 limits fill to 53% for one conductor, 31% for two, and 40% for three or more β leaving room to pull wires without damaging insulation or trapping heat.
Yes. Sizing up one trade size is common practice and gives you room for future conductors, as long as it doesn't create other installation issues.