What Gauge Wire for a 20-Amp Circuit?

A short decision page for a frequent shop question. The common copper association is 12 AWG under typical talk-shop conditions — not a permit drawing.

Open AWG tool Full ampacity chart

Reference only. Permanent wiring must follow local code and listings. When in doubt, hire a licensed electrician. Disclaimer

Decision table

Question Common copper association Notes
20A branch-style question 12 AWG Common residential copper association only — verify code, temperature, and install method.
15A branch-style (for contrast) 14 AWG Often associated with 15A copper — do not put 14 AWG on a 20A breaker based on this page.
Decision flow for 20 amp wire selection from copper material through length check to 12 AWG or 10 AWG copper
Simplified decision flow for 20 amp copper branch circuits — educational reference only.

12 AWG vs 14 AWG at a glance

Cross-section comparison of 12 AWG copper wire at 2.053 mm versus 14 AWG at 1.628 mm for 20 amp versus 15 amp circuits
Cross-sections drawn to relative scale — 12 AWG is 26% larger in diameter, 59% more area.

Primary for 20A talk

12 AWG

≈ 0.0808" · 2.05 mm

Often associated with 20A copper branch (conditions apply)

Not the 20A default

14 AWG

≈ 0.0641" · 1.63 mm

Often associated with 15A copper branch (conditions apply)

Boundaries

  • Aluminum branch wire and multi-wire assemblies need their own tables — not this page.
  • Long temporary cords: use load + length, not only “20A → 12 AWG”.
  • Device, receptacle, and breaker listings can restrict conductor size independently.

Product match (restrained)

If you only need a short length of copper for a shop experiment or repair kit — not a whole-house feeder — this sample-length 12 AWG product matches the label above. Confirm AWG on the listing. We do not push whole-house cable from this page.

FAQ

What gauge wire for a 20 amp circuit?

In common US residential copper branch talk, 20 amp is often associated with 12 AWG copper under typical conditions. That is an educational association only — temperature rating, insulation type, length, and local code can change the answer. Confirm with code and a qualified electrician for permanent wiring.

Can I use 14 AWG on a 20 amp breaker?

Do not treat this page as permission. In many US residential contexts, 14 AWG copper is associated with 15A protection, not 20A. Always follow the breaker, device listings, and code — never upsize the breaker on thinner wire based on a web chart.

Is 12 AWG always enough for 20 amp tools?

For temporary extension cords, length and load matter as much as AWG. Long runs can need a heavier cord class. Use the extension cord gauge helper for load + length, not only this branch-style note.

Is this advice a substitute for local electrical code / licensed electrician?

No. Workshop Ref publishes reference tables and finders for education only — not code-compliance verification or wiring design. Permanent branch circuits must follow local code and the work of a licensed electrician where required. Treat the 12 AWG association above as a starting question to bring to code, not an answer to skip inspection.

What about long runs — does 20 amp always stay on 12 AWG?

Not always. NEC 210.19(A)(1) Informational Note recommends keeping voltage drop at or below about 3% on a branch circuit (5% total with feeders). On a long run to a detached garage or outbuilding, voltage drop can push the next size up — commonly 10 AWG copper for that length. Use the AWG ampacity tool with your actual one-way length before buying.

Related

Wire hub · Wire gauge chart · AWG gauge chart · Ampacity chart · AWG tool · Extension cord gauge

See the site disclaimer.