Conduit Fill Calculator
Calculate NEC-compliant conduit sizing instantly. Supports EMT, RMC, IMC, PVC, and FMC with automatic fill percentage calculations.
Use Calculator in AppWhat is Conduit Fill?
Conduit fill refers to the maximum percentage of a conduit's internal area that can be occupied by electrical conductors. The NEC limits conduit fill to prevent overheating and allow for easy wire pulling during installation.
Proper conduit sizing ensures conductors can dissipate heat effectively and can be installed or replaced without damage to wire insulation.
NEC Conduit Fill Percentages
Per NEC Chapter 9, Table 1, the maximum conduit fill depends on the number of conductors:
Single conductor fill limit
Two conductor fill limit
Three or more conductors
EMT Conduit Fill Areas (Square Inches)
| Trade Size | Total Area | 1 Wire (53%) | 2 Wires (31%) | 3+ Wires (40%) |
|---|---|---|---|---|
| 1/2" | 0.304 | 0.161 | 0.094 | 0.122 |
| 3/4" | 0.533 | 0.283 | 0.165 | 0.213 |
| 1" | 0.864 | 0.458 | 0.268 | 0.346 |
| 1-1/4" | 1.496 | 0.793 | 0.464 | 0.598 |
| 1-1/2" | 2.036 | 1.079 | 0.631 | 0.814 |
| 2" | 3.356 | 1.779 | 1.040 | 1.342 |
| 2-1/2" | 5.858 | 3.105 | 1.816 | 2.343 |
| 3" | 8.846 | 4.688 | 2.742 | 3.538 |
THHN/THWN Wire Areas (NEC Chapter 9 Table 5)
| Wire Size (AWG) | Area (sq. in.) | Wire Size | Area (sq. in.) |
|---|---|---|---|
| 14 AWG | 0.0097 | 2 AWG | 0.1158 |
| 12 AWG | 0.0133 | 1 AWG | 0.1562 |
| 10 AWG | 0.0211 | 1/0 AWG | 0.1855 |
| 8 AWG | 0.0366 | 2/0 AWG | 0.2223 |
| 6 AWG | 0.0507 | 3/0 AWG | 0.2679 |
| 4 AWG | 0.0824 | 4/0 AWG | 0.3237 |
Conduit Fill Example
Problem:
What size EMT conduit is needed for 4 #12 AWG THHN conductors and 1 #12 AWG ground?
Solution:
Total conductors: 5 × #12 THHN = 5 × 0.0133 = 0.0665 sq. in.
Fill allowed (3+ wires): 40%
From EMT table: 1/2" EMT allows 0.122 sq. in. at 40%
Use 1/2" EMT (0.0665 < 0.122)
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