Tools · Conduit Fill
Conduit Fill Calculator
Check raceway fill against NEC Chapter 9 for THHN/THWN-2 and XHHW-2 conductors in EMT, IMC, Rigid, or PVC — and see the smallest conduit that fits, for every conduit type at once.
How it’s calculated. NEC Chapter 9, Table 1 maximum fill: 53% for one conductor, 31% for two, 40% for three or more — or 60% for a nipple ≤24″ (Note 4), selectable above. Conductor areas are from Table 5 for THHN/THWN-2 and XHHW-2 (XHHW-2 runs noticeably fatter on small sizes — a #12 is ~36% bigger than THHN, so the type matters); conduit internal areas are from Table 4 (EMT, IMC, Rigid, PVC Sch 40 & 80). The “smallest that fits” rows show the smallest trade size within the allowed fill — for the selected conduit and for every type at once.
More than three current-carrying conductors in one raceway also requires an ampacity adjustment per NEC 310.15(C)(1) — the calculator flags this, and the Wire Ampacity calculator applies it. Verify equipment-grounding and derating requirements against the full design.
Need it engineered and stamped?
Routing raceway and distribution on a bigger job? We’re a commercial electrical contractor in Tucson — we engineer it, pull the permits, and self-perform the install.
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