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Amperage to Wire Gauge Calculator

Find the minimum copper wire gauge rated to safely carry a given amp load, per standard NEC ampacity tables.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax

Minimum wire gauge

12 AWG

High confidence

This is ampacity-only sizing — long runs may also need a thicker gauge to control voltage drop (see the Wire Gauge Voltage Drop Calculator).

Ampacity of recommended gauge
20 A

With the figures above, the minimum wire gauge comes to 12 AWG. This is presented for United States. Building in another market? Change the selector above and the units and terminology follow.

Add the equipment this sizes

This result is a specification — 12 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 — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • Standard copper conductor ampacity (NEC Table 310.16, 60°C column, typical for residential NM-B cable): 14 AWG=15A, 12 AWG=20A, 10 AWG=30A, 8 AWG=40A, 6 AWG=55A, 4 AWG=70A

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Frequently asked questions

Why does this use the 60°C ampacity column?
The 60°C column is the standard reference for common residential NM-B (Romex) cable terminations, which is the most common household wiring type — different cable types, insulation ratings, or ambient conditions can use higher ampacity columns.
Should I size wire to the breaker or to the device?
Always size wire to the breaker's rating (or the maximum overcurrent protection you intend to install), not just the specific device you're powering today — this protects the circuit even if a higher-draw device is added later.
Does bundling multiple wires in one conduit change this?
Yes — bundling several current-carrying conductors together requires an ampacity derating per NEC 310.15(C)(1), which can require a thicker gauge than this single-conductor estimate shows. An electrician accounts for this in a full circuit design.