Conduit Fill Calculator
Calculate conduit fill percentage and maximum wire count per NEC 40% fill rule. Supports standard conduit sizes.
How It Works
Calculate conduit fill percentage and maximum wire count per NEC 40% fill rule. Supports standard conduit sizes. Enter your values above and click Calculate to get instant results.
Formula
Fill% = (wire_area × count) / conduit_area × 100 | NEC max: 40% for 3+ wires
Quick Examples
- 3× AWG-12 in 1/2" conduit → 22.5% fill (pass)
- 6× AWG-12 in 1/2" conduit → 45% fill (fail)
Frequently Asked Questions
What is the NEC conduit fill rule?
NEC 310.15 limits conduit fill to 40% for 3 or more wires, 31% for 2 wires, and 53% for 1 wire to allow heat dissipation and ease of wire pulling.
What conduit type are these figures for?
This calculator uses standard EMT (electrical metallic tubing) trade sizes. Values are based on NEC Annex C fill tables for THWN-2 wire.