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What Size Wire for 20 Amps?

For a non-continuous 20 amp load under the default short-run assumptions, start with 12 AWG copper or 10 AWG aluminum. This is the common branch-circuit page where the 12 AWG copper small-conductor limit is the key constraint.
Load
20 A
Distance
0 ft entered
Band
Branch circuit
Defaults
Non-continuous, 75 C lugs, 86 F, 240 V single-phase
Conductor count
3 current-carrying

Computed Starting Point

The table uses common defaults. Change the calculator inputs for the actual installation.

MaterialComputed sizeOCPDUsable ampacityGoverning constraintDefault check
Copper12 AWG20 A20 ASmall conductor overcurrent limitPasses defaults
Aluminum10 AWG20 A25 ASmall conductor overcurrent limitPasses defaults
What Size Wire for 20 Amps? under common non-continuous defaults: THHN or XHHW-2 insulation, 75 C terminations, 86 F ambient, 240 V single-phase, no more than three current-carrying conductors, and 0 ft route length entered.

What 20 A ChangesAt 20 A, the non-continuous default copper result is 12 AWG and is capped at 20 A by the small-conductor limit. Aluminum appears as 10 AWG under the calculator defaults, but aluminum is uncommon for this branch-circuit use case.

Run the wire size calculator

Adjacent Amp Ratings

See whether stepping one standard size up or down forces a conductor jump under the same defaults.

LoadCopper sizeCopper OCPDAluminum sizeAluminum OCPD
15 A14 AWG15 A12 AWG15 A
20 A (this page)12 AWG20 A10 AWG20 A
25 A10 AWG25 A10 AWG25 A
Copper and aluminum starting sizes for 20 A and the neighboring published amp pages, under the same defaults as the result above.

A plateau means neighboring amp ratings share a conductor size under these defaults. A jump means a standard breaker change often needs a larger wire; confirm with your real ambient, length and terminations.

20 A Is the Common Branch-Circuit Step

Branch circuit context for a 20 A circuit.

A 20 A wire-size search usually comes from receptacle circuits, kitchen or laundry small-appliance circuits, garage outlets, bath loads, or a dedicated tool or equipment branch. The search intent is often practical: can this be 12 AWG copper, and what changes from 15 A?

Under the non-continuous defaults on this page, 20 A is still small-conductor governed. The important adjacent contrast is that 15 A uses 14 AWG copper, while 25 A moves copper up to 10 AWG.

What Changes This Answer

Checks that can change the starting conductor under the displayed defaults.

  • Keep 12 AWG on the 20 A page

    Do not use the 15 A copper answer for a 20 A breaker. Under these defaults, the page moves from 14 AWG copper at 15 A to 12 AWG copper at 20 A.

  • Do not round 25 A down

    The adjacent 25 A page changes the copper result to 10 AWG under the same defaults.

  • Check receptacle and equipment rules

    A generic 20 A conductor answer does not replace device ratings, equipment instructions or circuit-specific rules.

  • Rerun continuous loads

    The displayed answer does not apply the 125 percent continuous-load multiplier. A true 20 A continuous load moves beyond this amp-only default.

  • Use distance for long branches

    The amp-only answer assumes no route length. Long 120 V or 240 V runs should be checked with the wire-size calculator.

20 Amp Wire Size FAQs

What size wire for 20 amps?
Under the non-continuous defaults on this page, start with 12 AWG copper or 10 AWG aluminum. Both are shown with a 20 A overcurrent device; continuous loads should be rerun with the continuous setting enabled.
Why is 20 A different from 15 A?
The 15 A page lands on 14 AWG copper under these defaults. A 20 A branch circuit moves to 12 AWG copper.
Can I use 12 AWG copper for 25 amps?
Not under this page's small-conductor limit. The 25 A page moves to 10 AWG copper.
Does aluminum make sense for a 20 A branch circuit?
Usually not in ordinary branch-circuit work. The calculator shows an aluminum starting point, but the equipment and terminals still need to be listed for aluminum.