Conduit Fill
Percent fill by conduit type and conductor count.
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
Checked against published worked examples from: NFPA.
Details, formula, and sources
Formula or tableConductor cross-sectional area sum / interior conduit area, compared to NEC Chapter 9 Table 1 fill limits (53% / 31% / 40% for 1, 2, ≥ 3 conductors).
Source and editionNEC 2023 (NFPA 70). Chapter 9 Tables 1, 4, 5.
Free accessFree read-only access at nfpa.org/freeaccess.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesconduit, 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