Conduit Fill

Percent fill by conduit type and conductor count.

Run the calculator

Example

You enter

Conduit type EMT
Trade size 3/4
Conductors insulation THHN, AWG 12, count 4

You get

Fill 0.0532
Conduit area (in²) 0.533
Fill (%) 9.98
Threshold (%) 40
Pass Yes
Count 4

Details, formula, and sources

Conductor cross-sectional area sum / interior conduit area, compared to NEC Chapter 9 Table 1 fill limits (53% / 31% / 40% for 1, 2, ≥ 3 conductors).

NEC 2023 (NFPA 70). Chapter 9 Tables 1, 4, 5.

Free read-only access at nfpa.org/freeaccess.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: conduit, trade_size, conductors, fill_in2, conduit_area_in2, fill_percent, threshold_percent, pass, count

Conductor area data NEC Chapter 9 Table 5 (THHN/THWN-2)NEC 2023
Conduit area data NEC Chapter 9 Table 4NEC 2023 trade-size internal areas