Conduit Fill Calculator

Inputs

Conduit typeTrade sizeConductor sizeTHHN/THWN-2 area from NEC Chapter 9, Table 5Number of conductorsCount every conductor, including the equipment grounding conductor

Result

Within the fill allowance

Fill

13.1 %

Limit

40 %

Max conductors

Calculation steps

Conduit internal area
0.304 sq in
Ref: NEC Chapter 9, Table 4
Conductor area (each)
0.0133 sq in
Ref: NEC Chapter 9, Table 5 (THHN/THWN-2)
Fill limit
40 %
Ref: NEC Chapter 9, Table 1
Total conductor area
0.0133 x 3
0.0399 sq in
Actual fill percentage
Total conductor area / conduit area x 100
13.1 %
Maximum identical conductors
9
Ref: NEC Chapter 9, Table 1 and Note 7

Export

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These calculators are provided for educational, design-planning and general informational purposes only. They do not constitute professional engineering advice or a recommendation for licensed installation. Codes and electrical regulations vary by jurisdiction, and actual installation must be carried out by a licensed electrician in accordance with the code enforced locally. Misuse of these results can cause electrical fire, equipment damage or code violations. The NEC table values on this site reflect NEC 2023; the 2026 edition has not been verified. Verify every value against the edition of the NEC in force in your area.