About Pull Box Sizing Calculator

A free NEC 314.28 compliance tool built for electricians, contractors, and inspectors who need accurate pull box dimensions fast.

Why This Tool Exists

Pull box sizing under NEC Article 314.28 is straightforward once you know the formulas — but working through them by hand on a job site, with conduit sizes in mixed trade designations and multiple conduits entering the same wall, takes more time than it should. Errors are easy to make, and undersized boxes fail inspection.

We built this calculator to give electricians, master electricians, electrical engineers, and inspectors an instant, reliable answer. Enter your conduit trade sizes and pull configuration; get back the NEC-minimum box dimensions and a recommended standard NEMA size. No account required, no ads in your way.

The tool handles all three NEC 314.28 configurations — straight pulls (Article 314.28(A)(1)), angle pulls (314.28(A)(2)), and U-pulls — across all standard conduit trade sizes from ½″ through 6″, covering EMT, IMC, RMC, and PVC conduit.

Code-Accurate Formulas

All calculations are taken directly from NFPA 70, National Electrical Code, 2023 Edition, Article 314.28. We cross-reference against Mike Holt Enterprises NEC commentary and Ugly's Electrical References pull box sizing tables.

Built for the Field

Electricians and inspectors need answers in seconds, not minutes. This tool is fast, mobile-friendly, and works without any login or subscription. It's a tool that earns a spot in your browser bookmarks.

Verified & Maintained

We verify our calculations against NEC code cycles and update the tool when standards change. All results include the specific NEC section and the formula used so you can verify the work yourself.

Sources & Methodology

The pull box sizing formulas are derived from:

  • NFPA 70 — National Electrical Code (NEC), 2023 Edition, Article 314.28 — the primary standard governing pull and junction box sizing
  • Mike Holt Enterprises — NEC 314.28 pull box sizing commentary and worked examples
  • Ugly's Electrical References, 2023 Edition — pull box sizing tables and conduit trade size reference

Standard NEMA pull box size recommendations are based on common off-the-shelf dimensions from major manufacturers. All calculations are deterministic — the same inputs always produce the same outputs — and the formula used is displayed with every result.

Important: This tool provides NEC minimum sizing for informational purposes. Always verify pull box installations with a licensed electrician and the Authority Having Jurisdiction (AHJ) for your location. Some jurisdictions adopt local amendments to the NEC that may require larger dimensions.

Get in Touch

Found a calculation error, have a question about NEC 314.28, or want to suggest an improvement?

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