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Extension Cord Gauge Calculator

Find the thinnest extension cord gauge that keeps voltage drop under 3% for your tool's amp draw and cord length.

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 2026-08-25 · v1.0.0

Market
Imperial · sales tax
49.21 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Recommended cord gauge

14 AWG

High confidence
Voltage drop at recommended gauge
2.57 %

With the figures above, the recommended cord gauge comes to 14 AWG. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 14 AWG — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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

  • Standard single-phase voltage drop formula: Vdrop = (2 x K x length in ft x amps) / circular mils, K=12.9 for copper — the same physics used to size branch-circuit wiring, applied here to cord length
  • 3% voltage drop is a widely used comfort threshold for extension cords to avoid overheating and underpowered tools

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 not just always use the thickest cord?
Thicker (lower-gauge) cords are heavier, stiffer, and more expensive — this finds the thinnest cord that's still safe and efficient for your specific length and load, rather than over-specifying.
What happens if I use a gauge that's too thin?
Excess voltage drop makes motorized tools run hotter, weaker, and less efficiently, and can cause the cord itself to heat up under sustained load — a real fire risk with heavy-draw tools on long, thin cords.
Does cord length include the tool's own built-in cord?
No — this is for the extension cord only. Add the extension cord's length to any other extension cords used in series, but the tool's own short cord is usually negligible for this calculation.