Free calculator · AstralLearn
Conduit fill calculator
Pick your conduit and conductors and see the NEC Chapter 9 fill percentage — plus the smallest conduit that fits. Free, no sign-up.
Back to AstralLearnConductors
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Fits
10%limit 40%
fill of conduit area4 conductors → 40% rule
- Used area
- 0.0532 in²
- Allowed area
- 0.2132 in²
How it works: NEC Chapter 9 limits fill to 53% (1 conductor), 31% (2), or 40% (3 or more) of the conduit's internal area. We add up each conductor's area (Table 5) against the conduit's area (Table 4).
Educational reference — verify against the current NEC and your AHJ. Want it done right and permitted? Call a licensed C-10 → (650) 562-8594.
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