THHN (Thermoplastic High Heat-resistant Nylon-coated) and its dual-rated variant THWN are the most common conductor insulation types for conduit installations in commercial, industrial, and residential work. The nylon jacket makes THHN conductors easy to pull and resistant to oil and gasoline. For conduit fill calculations, THHN conductor cross-sectional areas come from NEC Chapter 9, Table 5 — for example, 14 AWG THHN is 0.0097 sq in, 12 AWG is 0.0133 sq in, 10 AWG is 0.0211 sq in, 8 AWG is 0.0366 sq in, and 6 AWG is 0.0507 sq in. This calculator handles any combination of THHN conductor sizes.
1" EMT (0.864 sq in internal area): 40% fill = 0.346 sq in. Six 10 AWG THHN conductors: 6 × 0.0211 sq in = 0.127 sq in. Fill = 14.7%. Within 40% limit. Could fit up to 16 conductors of 10 AWG THHN.
This is a variant of the full Conduit Fill Calculator — which supports EMT, PVC, RMC, IMC, and flexible conduit with any conductor type and size.
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