Tools · Conduit Fill
Conduit Fill Calculator
Check raceway fill against NEC Chapter 9 for THHN/THWN-2 conductors in EMT, IMC, Rigid, or PVC — and see the smallest conduit that fits.
How it’s calculated. NEC Chapter 9, Table 1 maximum fill: 53% for one conductor, 31% for two, 40% for three or more. Conductor areas are THHN/THWN-2 (Table 5); conduit internal areas are from Table 4 (EMT, IMC, Rigid, PVC Sch 40 & 80). The “smallest that fits” is the smallest trade size of the selected conduit that stays within the allowed fill.
Assumes a standard raceway (not a nipple ≤24″, which permits 60%) and all conductors of the THHN/THWN-2 dimension. Verify equipment-grounding and derating requirements against the full design.
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