Conduit Fill Chart
NEC Chapter 9, Table 1 limits how much of a conduit's internal area can be filled with conductors: 53% for 1 conductor, 31% for 2, and 40% for 3 or more. The tables below show conduit internal areas and conductor cross-sectional areas to help you check fill manually or understand calculator results.
NEC Fill Limits
| Number of Conductors | Max Fill % | Notes |
|---|---|---|
| 1 | 53% | Single conductor (e.g., service entrance cable) |
| 2 | 31% | 2-wire circuit |
| 3 or more | 40% | Most branch circuits and feeders |
Conduit Internal Areas (NEC Chapter 9, Table 4)
| Trade Size | EMT (sq in) | 40% Fill (sq in) | PVC Sch40 (sq in) | 40% Fill (sq in) | RMC (sq in) | 40% Fill (sq in) |
|---|---|---|---|---|---|---|
| 1/2" | 0.304 | 0.122 | 0.285 | 0.114 | 0.314 | 0.126 |
| 3/4" | 0.533 | 0.213 | 0.508 | 0.203 | 0.549 | 0.220 |
| 1" | 0.864 | 0.346 | 0.832 | 0.333 | 0.887 | 0.355 |
| 1-1/4" | 1.496 | 0.598 | 1.453 | 0.581 | 1.526 | 0.610 |
| 1-1/2" | 2.036 | 0.814 | 1.986 | 0.794 | 2.071 | 0.828 |
| 2" | 3.356 | 1.342 | 3.291 | 1.316 | 3.408 | 1.363 |
| 2-1/2" | 5.858 | 2.343 | 4.695 | 1.878 | 4.866 | 1.946 |
| 3" | 8.846 | 3.538 | 7.268 | 2.907 | 7.499 | 3.000 |
| 4" | 14.753 | 5.901 | 12.554 | 5.022 | 12.882 | 5.153 |
Approximate values from NEC Chapter 9, Table 4. Verify with current NEC edition.
THHN/THWN-2 Conductor Areas (NEC Chapter 9, Table 5)
| Conductor | Area (sq in) |
|---|---|
| 14 AWG THHN | 0.0097 |
| 12 AWG THHN | 0.0133 |
| 10 AWG THHN | 0.0211 |
| 8 AWG THHN | 0.0366 |
| 6 AWG THHN | 0.0507 |
| 4 AWG THHN | 0.0824 |
| 3 AWG THHN | 0.0973 |
| 2 AWG THHN | 0.1158 |
| 1 AWG THHN | 0.1562 |
| 1/0 AWG THHN | 0.1855 |
| 2/0 AWG THHN | 0.2223 |
| 3/0 AWG THHN | 0.2660 |
| 4/0 AWG THHN | 0.3237 |
| 250 kcmil THHN | 0.3970 |
| 350 kcmil THHN | 0.5281 |
| 500 kcmil THHN | 0.7073 |
Approximate values for THHN/THWN-2 from NEC Chapter 9, Table 5. Other insulation types (XHHW, RHH, etc.) have different areas.