Conduit Fill & Raceway Sizing Calculator
Instantly check if your wires will fit safely in a specific pipe size.
1Conduit Settings
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2Wire Schedule
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Area: 0.0109 × 3 = 0.0327 in²
COMPLIANTStatusFill is within safe limits.
Status
Fill is within safe limits.
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Total Used Area -
Total Used Area
The combined cross-sectional area of all conductors (wires).
Max Allowed Area (40%) -
Permitted Fill
The maximum conduit area you can occupy based on standard tables (53% for 1 wire, 31% for 2, 40% for 3+).
Total Internal Area (100%) -
Conduit Internal Area
The total available cross-sectional area inside the conduit (100% fill).
References
- Ch 9, Table 1:Max fill % rules
- Ch 9, Table 4:Conduit dimensions
- Ch 9, Table 5:Wire area (THHN/XHHW)
- Ch 9, Table 8:Bare conductor properties
Popular conduit fill Configurations
Conduit Fill Formula
Total Wire Area ≤ Raceway Area × Fill %
NEC Table 1 Limits
NEC Chapter 9 Table 1 sets the maximum fill percentage: 53% for 1 wire, 31% for 2 wires, and 40% for over 2 wires. This prevents damage during pulling and allows for heat dissipation.
Frequently Asked Questions
What is the 40% fill rule?
The 40% rule applies when installing more than 2 conductors in a raceway. You cannot use more than 40% of the pipe's internal area.
Can I put low voltage in the same pipe as 120V?
Generally, no. NEC 300.3(C)(1) allows it only if all conductors are rated for the maximum voltage present. However, Article 725 imposes stricter separation rules for Class 2/3 circuits to prevent interference and safety hazards.
Does the ground wire count for conduit fill?
Yes. Equipment grounding conductors must be counted when calculating fill, as they take up physical space in the raceway.