From this site

One project, every trade

Each calculator adds its lines to a single estimate — consolidated BOM, schedule and cash-flow included.

Open My Project →

Equipment Grounding Conductor Sizing Reference Calculator

Estimate a proportional equipment grounding conductor size from the circuit's overcurrent device rating.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Approximate grounding conductor sizing factor

2.25 (illustrative scaling units)

Low confidence

This proportional calculation is illustrative ONLY — NEC Table 250.122 defines equipment grounding conductor size using specific breakpoints (e.g. 60A→10AWG copper, 100A→8AWG copper, 200A→6AWG copper, 400A→3AWG copper), NOT a continuous formula. Always look up the required size directly from NEC Table 250.122 (or your local code) for the actual OCPD rating — never use a proportional/interpolated calculation for the real conductor size.

At the values currently entered, the approximate grounding conductor sizing factor works out to 2.25 (illustrative scaling units). Confidence on this run is low: check the result against a supplier quote or a professional before ordering or building. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • NEC Table 250.122 sets equipment grounding conductor size based on the rating of the automatic overcurrent device ahead of the circuit — sizes step up at defined breakpoints rather than scaling continuously. This calculator applies a simplified proportional approximation (OCPD rating × a scaling factor) as a rough estimate only; the actual required size MUST be taken directly from NEC Table 250.122, not calculated proportionally.

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why is this calculator's result not a wire gauge?
NEC Table 250.122 sizes equipment grounding conductors using specific breakpoints (e.g. 60A→10 AWG copper, 100A→8 AWG copper, 200A→6 AWG copper, 400A→3 AWG copper), not a continuous formula, so a proportional calculation like this one cannot produce an actual wire gauge — it only illustrates how sizing roughly scales with OCPD rating.
Can I use this result to select my actual grounding conductor?
No. Always look up the required size directly from NEC Table 250.122 (or your local code) for your actual OCPD rating — never use a proportional or interpolated calculation for the real conductor size.
What determines the equipment grounding conductor size in the real code table?
It's set by the rating of the automatic overcurrent device (fuse or breaker) ahead of the circuit — larger OCPD ratings require larger grounding conductors, stepping up at the specific breakpoints defined in NEC Table 250.122.