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Electrical Engineering & Inspection Utility

National Electrical Code (NEC) Conduit Fill Sizer

Calculate exact raceway fill percentages, mixed conductor bundle areas, jam ratios, and minimum compliant trade sizes according to official NFPA 70 / NEC Chapter 9 Tables 1, 4, 5, and 8.

Every figure is calculated in your browser. No project or conductor schedule data is transmitted or stored.

Standard Electrical Presets:Common service entrance, subpanel, and branch circuit configurations.
Compliance StatusCOMPLIANTMeets NEC Chapter 9 Table 1
Actual Conduit Fill20.8%of 40% allowable limit
Total Conductor Area0.6997sq inches (4 wires)
Minimum Trade Size1-1/2"for EMT

1. Conduit & Raceway Specifications

2. Conductor Schedule (Tables 5 & 8)

Add mixed gauges and insulations. Fill area calculated automatically.

Single Area: 0.2223 sq in (O.D. 0.532")Total: 0.6669 sq in
Single Area: 0.0328 sq in (O.D. 0.204")Total: 0.0328 sq in

Cross-Section Visualizer

2" EMT
20.8% Fill
Conduit I.D.:2.067"
Total Conduit Area:3.356 sq in
Max Allowed Area (40%):1.342 sq in
Remaining Free Area:0.643 sq in

Inspector Submittal PDF

Generate an official NEC Chapter 9 submittal sheet with complete mathematical breakdowns for building officials.

NEC Chapter 9 Table 1 Conduit Fill Rules Explained

The National Electrical Code (NEC) establishes maximum raceway fill percentages in Chapter 9, Table 1 to prevent heat buildup and physical damage to wire insulation during pulling:

1 Conductor: 53%

Single conductors have no other wires to bind against, allowing up to 53% of raceway cross-sectional area.

2 Conductors: 31%

Two conductors pull in an oval configuration that can bind against conduit walls, strictly limited to 31%.

3+ Conductors: 40%

Three or more wires form a natural cluster, permitted up to 40% maximum cross-sectional area.

Nipple Exception (Note 4): Where conduit or tubing does not exceed 24 inches (600 mm) in length, the raceway is permitted to be filled to 60% of its total cross-sectional area, and ampacity derating factors (310.15(C)(1)) do not apply.

How to use this tool

  1. Choose the conduit type and trade size

    EMT, PVC Schedule 40 or Schedule 80, and the trade size you intend to run. Schedule 80 has a thicker wall, so it holds fewer conductors than Schedule 40 at the same size.

  2. Add every conductor in the raceway

    Insulation type, AWG size and count per group. Equipment grounding conductors count toward fill whether bare or insulated.

  3. Check fill against the limit

    The tool works from NEC Chapter 9 Tables 1, 4, 5 and 8 and shows fill as a percentage of the 40% limit for three or more conductors.

  4. Check the jam ratio and export

    Three same-size conductors in a bend jam when the conduit-to-cable diameter ratio falls near 2.8 to 3.2. Download the submittal PDF for the inspector.

Frequently Asked Questions

Does the grounding conductor count toward conduit fill?

Yes. All equipment grounding conductors, whether bare or insulated, must be included when calculating total conductor cross-sectional area for conduit fill under NEC Chapter 9.

Why do PVC Schedule 40 and Schedule 80 hold different numbers of wires?

PVC Schedule 80 has a significantly thicker wall than Schedule 40 to provide physical impact resistance. Because the outside diameter remains identical, Schedule 80 has a smaller inside diameter (I.D.) and less internal cross-sectional area, requiring larger trade sizes for the same wire bundle.

Are my electrical calculations confidential?

Yes, 100%. All NEC Table 4 and 5 calculations, fill formulas, jam ratios, and PDF submittals execute strictly inside your local browser memory using client-side JavaScript. Zero project specifications are ever transmitted to any remote server.

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