Free Conduit Fill Calculator
Check whether a set of conductors fits within a conduit according to NEC fill percentage rules.
sq in
sq in
Conduit Fill
45.0 %
NEC Max Fill40 %
Remaining Area-0.0436 sq in
Conduit Fill vs Conduit Internal Area
NEC Conduit Fill Rules
The National Electrical Code limits fill percentages to prevent overheating:
Calculate fill by dividing total conductor area (including insulation) by the conduit internal area.
Example Calculation
4 conductors of 12 AWG THHN (0.0973 sq in each) in 3/4-inch EMT (0.864 sq in).
- 01Total wire area = 4 x 0.0973 = 0.389 sq in
- 02Fill = 0.389 / 0.864 x 100 = 45.0%
- 03NEC allows 40% for 3+ conductors
- 04This conduit is overfilled; upsize to 1-inch EMT.
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