What Size Wire for a 20-Amp Breaker? 12 AWG Copper (2026)
The 20-amp circuit is the workhorse of American homes. It feeds your kitchen countertops, your bathroom receptacles, your garage, and most of the outlets a modern house cannot live without. This guide covers the exact wire size the NEC requires, why the answer is stricter than the ampacity tables suggest, how far you can run the cable, and which receptacles and protection each circuit needs.
Quick answer
A 20-amp breaker needs 12 AWG copper wire at minimum, per NEC 2023 Table 310.16 and the small-conductor cap in 240.4(D). For aluminum or copper-clad aluminum, the minimum is 10 AWG. 14 AWG copper is never allowed on a 20-amp breaker, and runs past about 45 feet at 120 volts should step up to 10 AWG to stay under 3 percent voltage drop.
20-Amp Wire Size Quick Reference
| Item | Specification |
|---|---|
| Copper wire (minimum) | 12 AWG |
| Aluminum / copper-clad aluminum (minimum) | 10 AWG |
| Common cable | 12/2 NM-B with ground (yellow jacket) |
| Standard receptacle | NEMA 5-15R (two or more) or 5-20R |
| 240V receptacle | NEMA 6-20R |
| Max run, 12 AWG at 120V, 20A (3% drop) | about 45 feet |
| Max run, 12 AWG at 240V, 20A (3% drop) | about 93 feet |
| Max continuous load (125% rule) | 16 amps |
| 12/2 NM-B price (July 2026) | about $0.62 per foot |
Sources: NEC 2023 (NFPA 70) Table 310.16 and 240.4(D); Southwire 12/2 NM-B 250 ft roll at Home Depot, checked July 2026.
Why 12 AWG Is the Minimum for a 20-Amp Breaker
NEC Table 310.16 lists 12 AWG copper at 20 amps in the 60-degree column that applies to standard NM-B cable, 25 amps in the 75-degree column, and 30 amps in the 90-degree column. Reading that table alone, you might think 12 AWG could sit behind a 25-amp breaker. It cannot. NEC 240.4(D), the small-conductor rule, caps the overcurrent device for 12 AWG copper at 20 amps no matter which temperature column the insulation qualifies for. The same rule caps 14 AWG copper at 15 amps and 10 AWG copper at 30 amps. The higher table values are not wasted, though: they give you headroom for derating when cable runs through hot attics or gets bundled with other cables. For aluminum the numbers shift down a size. 12 AWG aluminum is capped at 15 amps, so a 20-amp aluminum circuit needs 10 AWG. In practice nearly every residential 20-amp branch circuit is wired with 12/2 NM-B copper cable, the one with the yellow jacket that color-codes the gauge.
Can You Use 14 AWG Wire on a 20-Amp Breaker?
No, and this is the most common wiring violation I see discussed in r/electricians threads about home inspections. 14 AWG copper is limited to a 15-amp breaker by 240.4(D). Put it on a 20-amp breaker and the wire can carry 33 percent more current than its rating without the breaker ever noticing. The breaker protects the wire, not the appliance, so an overloaded 14 AWG run just heats up quietly inside the wall until the insulation fails. The reverse swap is always legal: 12 AWG wire on a 15-amp breaker is fine, and plenty of electricians wire entire houses in 12 AWG so any circuit can be bumped to 20 amps later by changing only the breaker. If you find a 20-amp breaker feeding a circuit that contains any 14 AWG segment, even a short jumper in one junction box, the correct fix is a 15-amp breaker or rewiring the segment, never leaving it as is. Our breaker size calculator matches breaker and wire ratings for any load.
What Circuits in a House Are 20 Amps?
The NEC requires several 20-amp circuits by name. Section 210.11(C) mandates two 20-amp small-appliance circuits for the kitchen countertops, one 20-amp laundry circuit, and one 20-amp circuit for bathroom receptacles. Beyond the required ones, most electricians put garage receptacles, dishwashers, disposals, microwaves, and workshop outlets on their own 20-amp circuits because a 15-amp circuit trips too easily under those loads. Use our electrical load calculator to see how these circuits add up across a panel.
| Circuit | Cable | Notes |
|---|---|---|
| Kitchen countertop (two required) | 12/2 NM-B | GFCI, per NEC 210.11(C)(1) |
| Bathroom receptacles | 12/2 NM-B | GFCI, per 210.11(C)(3) |
| Laundry | 12/2 NM-B | Required by 210.11(C)(2) |
| Garage receptacles | 12/2 NM-B | GFCI required |
| Dishwasher | 12/2 NM-B | Dedicated, GFCI per 210.8(D) |
| Microwave | 12/2 NM-B | Dedicated circuit |
| Window AC or shop tool, 240V | 12/2 NM-B | NEMA 6-20R receptacle |
How Far Can You Run 12 AWG Wire on a 20-Amp Circuit?
Ampacity sets the minimum gauge, but distance decides whether the minimum is enough. The NEC recommends keeping voltage drop under 3 percent on a branch circuit. Voltage drop for a single-phase run is:
where L is the one-way length in feet, I is the current in amps, and R is 1.93 ohms per 1,000 feet for 12 AWG copper (NEC Chapter 9, Table 8). Worked example: a 70-foot run to a garage workbench pulling a 16-amp continuous load gives VD = (2 × 70 × 16 × 1.93) / 1000 = 4.3 volts. On a 120-volt circuit that is 3.6 percent, over the limit. Stepping up to 10 AWG (1.21 ohms per 1,000 feet) drops it to 2.7 volts, or 2.3 percent, which passes. Check your own run with the voltage drop calculator or size the whole circuit in one step with the wire size calculator.
| Wire | 120V at 20A | 120V at 16A | 240V at 20A |
|---|---|---|---|
| 12 AWG copper | about 45 ft | about 58 ft | about 93 ft |
| 10 AWG copper | about 74 ft | about 93 ft | about 149 ft |
Maximum one-way run lengths at 3 percent voltage drop. A 20-amp breaker stays at 20 amps even when the wire is upsized for distance.
Which Receptacles Go on a 20-Amp Circuit?
Here is a detail that surprises people: you do not need 20-amp receptacles on a 20-amp circuit. NEC 210.21(B)(3) allows standard 15-amp receptacles on a 20-amp circuit as long as the circuit serves two or more receptacles, and a single duplex outlet already counts as two. That is why nearly every kitchen and bathroom in America has ordinary-looking outlets on 20-amp circuits. The exception is a circuit feeding exactly one receptacle, such as a dedicated appliance outlet: that one must be a 20-amp NEMA 5-20R, the type with the sideways T slot on the neutral. For 240-volt 20-amp loads such as larger window air conditioners and some shop tools, the receptacle is a NEMA 6-20R fed by a double-pole 20-amp breaker with 12/2 cable, with the white wire re-marked as a hot at both ends.
How Many Outlets Can Be on One 20-Amp Circuit?
The NEC sets no numeric limit for receptacles on a residential 20-amp circuit. The commercial rule assigns 180 VA per receptacle, which works out to 13 receptacles on a 20-amp circuit, and that number doubles as a sensible ceiling at home. Most electricians stop at 8 to 10 so a space heater and a vacuum sharing one room do not trip the breaker. Remember the 125 percent rule too: any load running three hours or more, such as an EV trickle charger or a big aquarium heater, counts as continuous and caps the circuit at 16 amps. I wrote a separate breakdown in the outlets per circuit guide.
GFCI and AFCI Requirements for 20-Amp Circuits
Protection requirements follow the room, not the breaker size. NEC 210.8 requires GFCI protection for receptacles in kitchens, bathrooms, garages, unfinished basements, laundry areas, outdoors, and within 6 feet of any sink, which covers most of the 20-amp receptacle circuits in a modern home. NEC 210.12 layers AFCI protection on top for nearly all habitable rooms. You can meet both with a dual-function circuit breaker, which typically runs $40 to $60, or with a GFCI receptacle at the first outlet in the run plus an AFCI breaker. When a 20-amp circuit trips repeatedly on a GFCI device, resist the urge to swap in a standard breaker: the device is usually reporting a real leakage fault in an appliance or buried in a damp junction box.
NM-B Cable vs THHN in Conduit for 20-Amp Circuits
Inside walls, the default is 12/2 NM-B cable, and its ampacity is locked to the 60-degree column, which is exactly 20 amps for 12 AWG. Run individual 12 AWG THHN conductors through conduit instead, as you would for a detached garage or an exposed basement wall, and the 90-degree insulation gives you 30 amps of table ampacity to burn on derating. That headroom matters more than it sounds. Bundle more than three current-carrying conductors in one conduit and NEC 310.15(C) starts cutting ampacity: seven conductors in a raceway are derated to 70 percent, which takes 12 AWG THHN from 30 amps down to 21, still enough for a 20-amp breaker. The same seven-conductor bundle of NM-B would fail. Ambient heat works the same way, so a conduit run across a 45-degree Celsius attic loses roughly 13 percent of its rating. Two practical notes: conduit also needs to be sized for the wire count, which our conduit fill calculator handles per NEC Chapter 9, and outdoor or underground runs need conductors rated for wet locations, such as THWN-2 or UF-B cable, not plain NM-B, which is dry-location only.
Aluminum and Copper-Clad Aluminum for 20 Amps
Aluminum is legal for a 20-amp circuit at 10 AWG, and copper-clad aluminum follows the same sizing. You will rarely see either in new small branch circuits, because the copper saving at this gauge is small and the termination rules are strict. The 12 and 10 AWG aluminum branch wiring installed in the late 1960s and early 1970s caused connection fires when paired with devices designed for copper, and that history still shapes practice: aluminum today is used mainly for large feeders, where the savings are real. If your home has old small-gauge aluminum circuits, use only devices marked CO/ALR, apply antioxidant paste at terminations, and have connections checked by an electrician. If you are pricing that work, our electrician rate calculator shows typical hourly rates of $50 to $130 by state.
What Does It Cost to Wire a 20-Amp Circuit in 2026?
Materials are cheap; labor is not. A 250-foot roll of Southwire 12/2 NM-B sells for about $154 at Home Depot as of July 2026, which is roughly $0.62 per foot. A standard 20-amp single-pole breaker costs $5 to $15, a GFCI receptacle about $20, and a dual-function breaker $40 to $60. A typical new 20-amp circuit run from the panel, parts and labor, lands between $150 and $400 depending on wall access and distance, based on quotes discussed in r/HomeImprovement and r/electricians this year. If the panel itself has no free slots, the job grows into a panel project; see the panel replacement cost guide for those numbers.
Common Mistakes on 20-Amp Circuits
The classic mistake is upsizing a breaker to stop nuisance trips. If a 20-amp breaker trips under load, the circuit is overloaded or faulted, and a 30-amp breaker on 12 AWG wire simply removes the protection while the wire cooks. Second is the hidden 14 AWG splice: someone extends a 20-amp circuit with leftover 14 AWG cable, and the whole circuit becomes illegal. Third is backstabbed receptacles, the push-in connections on the back of cheap devices, which loosen under the heavier loads 20-amp circuits carry; use the screw terminals. Fourth is ignoring the continuous-load rule and running a 19-amp load for hours: the ceiling for anything continuous is 16 amps. Last, remember that upsizing wire for a long run never means upsizing the breaker. The breaker matches the load and protects the smallest conductor in the circuit.
Electrical work carries safety and legal risk. Verify any calculation with a licensed electrician familiar with your local code amendments before performing work. This article references NEC 2023; many jurisdictions still operate under NEC 2017 or 2020 or have local amendments, so always confirm with your local AHJ.
Frequently Asked Questions
What gauge wire do I need for a 20-amp breaker?
Can I use 14 gauge wire on a 20-amp breaker?
Can I use 12 gauge wire on a 15-amp breaker?
How many outlets can I put on a 20-amp circuit?
Can I use 15-amp outlets on a 20-amp circuit?
How far can I run 12 AWG wire on a 20-amp circuit?
What is 12/2 wire used for?
Does a 20-amp circuit need GFCI protection?
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Data sources: NEC 2023 (NFPA 70) Table 310.16, 240.4(D), 210.8, 210.11(C), and 210.21(B)(3); NEC Chapter 9 Table 8 conductor resistance; Southwire 12/2 NM-B pricing at Home Depot, July 2026; r/electricians and r/HomeImprovement field reports. Written by Munir Afridi, VoltFlow editorial team. Reviewed against NEC 2023 Articles 210, 240, and 310.