Conduit Fill Calculator
Calculate wire fill percentage for electrical conduit using NEC Chapter 9 tables as a reference. Supports EMT, IMC, rigid, and PVC.
Conduit Fill Calculator
Add Wires
Conduit fill percentage depends on wire count. More wires require smaller fill percentage to ensure safe installation and heat dissipation.
Conduit Fill Reference
A conduit fill calculator compares total conductor area with the allowable raceway fill percentage under NEC Chapter 9 Table 1.
Fill Limits
- 1 conductor: 53 percent
- 2 conductors: 31 percent
- 3 or more conductors: 40 percent
Basic Check
- find raceway area
- add conductor areas
- divide conductor area by raceway area
- compare the result with the allowed fill percentage
Why It Matters
- affects pullability
- affects conductor heating
- affects code compliance
Raceway Types
- EMT: common indoor metal raceway
- IMC: heavier metal raceway
- Rigid: heavy-duty threaded metal raceway
- PVC: nonmetallic raceway for many outdoor or underground uses
- PVC Schedule 80: heavier-wall nonmetallic raceway
- FMC: flexible metal raceway
Derating Note
Conduit fill and conductor ampacity derating are separate checks. A raceway may pass fill limits and still require ampacity adjustment for conductor count or temperature.
Conduit Internal Area (sq in) — 40% Fill Capacity
| Trade Size | EMT | IMC | Rigid | PVC 40 | PVC 80 | 40% Fill Limit |
|---|---|---|---|---|---|---|
| 1/2" | 0.384 | 0.382 | 0.346 | 0.494 | 0.386 | 0.198 |
| 3/4" | 0.596 | 0.591 | 0.533 | 0.762 | 0.601 | 0.305 |
| 1" | 0.864 | 0.859 | 0.785 | 1.107 | 0.881 | 0.443 |
| 1 1/4" | 1.237 | 1.231 | 1.142 | 1.580 | 1.274 | 0.632 |
| 1 1/2" | 1.496 | 1.476 | 1.379 | 1.917 | 1.549 | 0.767 |
| 2" | 2.165 | 2.117 | 2.000 | 2.827 | 2.290 | 1.131 |
| 2 1/2" | 3.548 | 3.476 | 3.356 | 4.596 | 3.770 | 1.838 |
| 3" | 4.909 | 4.794 | 4.668 | 6.362 | 5.263 | 2.545 |
| 3 1/2" | 6.426 | 6.282 | 6.159 | 8.353 | 6.993 | 3.341 |
| 4" | 8.085 | 7.901 | 7.753 | 10.561 | 8.840 | 4.224 |
Common Conductor Areas (sq in) — THHN Wire
| AWG Size | Area (sq in) | AWG Size | Area (sq in) |
|---|---|---|---|
| 14 AWG | 0.0097 | 1/0 AWG | 0.1855 |
| 12 AWG | 0.0133 | 2/0 AWG | 0.2223 |
| 10 AWG | 0.0211 | 3/0 AWG | 0.2679 |
| 8 AWG | 0.0366 | 4/0 AWG | 0.3237 |
| 6 AWG | 0.0507 | 250 kcmil | 0.3970 |
| 4 AWG | 0.0824 | 300 kcmil | 0.4608 |
| 2 AWG | 0.1158 | 350 kcmil | 0.5246 |
| 1 AWG | 0.1562 | 400 kcmil | 0.5867 |
Frequently Asked Questions
Per NEC Table 1: one conductor = 53%, two conductors = 31%, three or more = 40%. These limits ensure wires can be installed easily and cooled properly without overheating. Never exceed these percentages without code variance.
3/4" EMT has 0.596 sq in area. At 40% fill (3+ wires), you can fit 0.238 sq in of wires. With 12 AWG THHN (0.0133 sq in each), that's approximately 17 wires. However, practical limits (pulling feasibility) are typically 5-7 wires per conduit. Use this calculator as a quick planning reference before final code review.
(1) Find the conduit's internal area from NEC Chapter 9, Table 4. (2) Add up all wire areas from Table 5. (3) Divide wire area by conduit area and multiply by 100. If result exceeds 40% (for 3+ wires), upsize the conduit. This calculator does it instantly.
PVC is better for underground burial. EMT will rust unless heavily protected. PVC is corrosion-proof and rated for direct burial per NEC. For outdoor above-ground, rigid or PVC with mechanical protection is preferred over EMT.
Overfilled conduit makes wire installation extremely difficult, can damage insulation, traps moisture (causing corrosion), creates overheating from bundled wires, and violates code. Inspectors will fail the installation. Always upsize conduit to stay within NEC fill limits.
