Conduit Fill Calculator

Calculate NEC-compliant conduit sizing instantly. Supports EMT, RMC, IMC, PVC, and FMC with automatic fill percentage calculations.

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What 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:

53%
1 Conductor

Single conductor fill limit

31%
2 Conductors

Two conductor fill limit

40%
3+ Conductors

Three or more conductors

EMT Conduit Fill Areas (Square Inches)

Trade SizeTotal Area1 Wire (53%)2 Wires (31%)3+ Wires (40%)
1/2"0.3040.1610.0940.122
3/4"0.5330.2830.1650.213
1"0.8640.4580.2680.346
1-1/4"1.4960.7930.4640.598
1-1/2"2.0361.0790.6310.814
2"3.3561.7791.0401.342
2-1/2"5.8583.1051.8162.343
3"8.8464.6882.7423.538

THHN/THWN Wire Areas (NEC Chapter 9 Table 5)

Wire Size (AWG)Area (sq. in.)Wire SizeArea (sq. in.)
14 AWG0.00972 AWG0.1158
12 AWG0.01331 AWG0.1562
10 AWG0.02111/0 AWG0.1855
8 AWG0.03662/0 AWG0.2223
6 AWG0.05073/0 AWG0.2679
4 AWG0.08244/0 AWG0.3237

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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