Conduit Fill Calculator
NEC 40% fill (3+ wires). Find conduit size that holds N wires of given gauge.
Result
Required conduit
½"
5 × 0.0133 in² = 0.0665 in² needed.
- Wire count5
- Per-wire area0.0133 in²
- Total wire area0.0665 in²
- ½" fits up to9 wires (0.122 in² @ 40%)
- ¾" fits up to16 wires (0.213 in² @ 40%)
- 1" fits up to26 wires (0.346 in² @ 40%)
- 1¼" fits up to44 wires (0.598 in² @ 40%)
- 1½" fits up to61 wires (0.814 in² @ 40%)
- 2" fits up to100 wires (1.342 in² @ 40%)
- Recommended½"
Step-by-step
- NEC ch.9 table 1: ≥3 wires = 40% fill of conduit area.
- Required area = 5 × 0.0133 = 0.0665 in².
- Smallest conduit with fill capacity ≥ 0.0665: ½".
How to use this calculator
- Enter wire count + gauge.
- Read smallest conduit that meets 40% fill.
About this calculator
NEC chapter 9 table 1: when 3+ wires share conduit, total wire area cannot exceed 40% of conduit cross-section. Why: heat dissipation, pulling without damaging insulation. THHN wire areas (cross section): 14 AWG 0.0097 in², 12 AWG 0.0133 in², 10 AWG 0.0211 in². EMT conduit ½" allows 0.122 in² fill; ¾" allows 0.213; 1" allows 0.346.
Frequently asked
NEC 9-1: for 3+ wires. 1 wire allows 53% fill, 2 wires allow 31%. Heat + pulling friction set the limit.
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