Wire Gauge Chart
Lower gauge number means thicker wire and more current.
By Jonathan West · reviewed 2026-09-14 ·how we research these
American Wire Gauge (AWG) runs backwards from intuition: the smaller the number, the thicker the conductor. A 14 AWG wire is thinner than a 12, which is thinner than a 10. Every three steps down roughly doubles the cross-sectional area.
The wire size determines the maximum breaker you may fit, and never the other way around, and that relationship is what the whole chart is really about.
The Chart
These are the standard sizes for copper conductor in residential branch circuits at 60°C termination, which is what household devices are rated for.
| Wire size (AWG) | Max breaker | Typical use |
|---|---|---|
| 18 AWG | — | Low-voltage: thermostat, doorbell |
| 16 AWG | — | Light-duty extension cords |
| 14 AWG | 15 A | Lighting, bedroom and living-room receptacles |
| 12 AWG | 20 A | Kitchen, bathroom, laundry, garage, outdoors |
| 10 AWG | 30 A | Electric dryer, water heater, window AC |
| 8 AWG | 40 A | Electric range, small subpanel |
| 6 AWG | 55 A | Large range, EV charger, subpanel |
| 4 AWG | 70 A | Subpanel, large service feeder |
| 2 AWG | 95 A | Service entrance, large subpanel |
The Rule That Matters
A breaker protects the wire. It does not protect the appliance. It is sized so that it trips before the conductor can overheat inside a wall.
This is why fitting a 20-amp breaker to a circuit wired in 14 AWG is dangerous rather than merely non-compliant. The 14 AWG cable is rated for 15 amps. The 20-amp breaker will happily pass 19 amps indefinitely, and the wire heats up in a cavity you cannot see, next to insulation and timber.
The corollary is useful: you can always fit a smaller breaker than the wire allows. Running 12 AWG on a 15-amp circuit is fine and gives you headroom to upgrade later.
Never increase a breaker size to stop nuisance tripping without confirming the wire supports it. Check the gauge printed along the cable sheath. If it says 14, the circuit is a 15-amp circuit regardless of what breaker someone fitted.
Distance Changes the Answer
The chart above assumes short runs. Over distance, resistance in the conductor causes voltage drop. The appliance receives less than 120 V, motors run hot and inefficiently, and lights dim.
The usual design target is to keep voltage drop under 3 percent on a branch circuit. Past roughly 50 feet on a 15- or 20-amp circuit, and much sooner on higher-current runs, going up one gauge is the standard remedy.
- Detached garages and sheds are where this bites most often. A 100-foot run to an outbuilding routinely needs a size up from the chart.
- 240 V circuits tolerate distance better than 120 V for the same power, because the current is halved.
- Voltage drop is not a code violation in most cases. The NEC treats 3% as a recommendation rather than a requirement. It is still poor practice to ignore.
| Circuit | Wire | Upsize beyond roughly |
|---|---|---|
| 15 A | 14 AWG | 50 ft |
| 20 A | 12 AWG | 60 ft |
| 30 A | 10 AWG | 75 ft |
| 40 A | 8 AWG | 90 ft |
| 50 A | 6 AWG | 110 ft |
Copper and Aluminum Are Not the Same
Aluminum conducts less well than copper, so it needs to be roughly two gauge sizes larger to carry the same current. Where copper 12 AWG handles 20 amps, aluminum needs 10 AWG.
Aluminum is still normal and correct for large feeders and service entrances, where the cost saving is large. What causes trouble is aluminum branch wiring, used widely in US homes built between roughly 1965 and 1973. It expands and contracts more than copper, which loosens terminations over time, and loose terminations arc. It has a documented association with house fires.
If you have aluminum branch circuits, do not simply fit standard devices. Connections require CO/ALR-rated devices or approved copper pigtail connectors, and this is properly electrician work.
Copper or Aluminum Wiring, and What to Do About It
Builders used aluminum branch wiring widely in US homes built roughly between 1965 and 1973 because aluminum wire costs less than copper as a raw material. Aluminum remains normal and correct for large feeders and service entrance conductors, but copper is the reliable standard for branch circuits feeding ordinary outlets and switches. Aluminum conducts electricity less effectively than copper, and it has a higher rate of thermal expansion and contraction. Repeated heating and cooling cycles at termination points cause connections to loosen over time, and a loose termination arcs and overheats.
A full rewire is not the only way to address aluminum branch wiring. Standard remediation offers two accepted paths, both handled by a licensed electrician. The primary method is pigtailing, where the electrician splices a short length of copper wire onto the aluminum conductor using an approved CO/ALR-rated connector, and the outlet or switch is then wired directly to the copper. The second option is installing replacement switches and outlets that are themselves rated CO/ALR, which are approved for direct connection to aluminum conductors.
This is not a DIY project. Loose or improperly matched connections on aluminum branch circuits are exactly what causes the arcing in the first place, so the fix belongs to a licensed electrician. Some home insurers also ask about or require inspection or remediation of aluminum branch wiring as a condition of issuing or renewing a policy, which makes professional remediation worth arranging even before a problem shows up.
| Factor | Copper Branch Wiring | Aluminum Branch Wiring |
|---|---|---|
| Relative material cost | Costs more as a raw material | Costs less than copper as a raw material |
| Gauge needed for 20 A | 12 AWG carries 20 amps | Roughly 10 AWG needed to carry the same 20 amps |
| Known failure mode | Terminations stay tight under normal conditions | From roughly 1965 to 1973 vintage, expansion and contraction loosens terminations, which arc and overheat |
| Remediation options | None needed | Pigtailing with an approved CO/ALR-rated connector, or CO/ALR-rated devices, fitted by a licensed electrician |
| Insurance angle | Standard coverage, no inspection required | Some insurers require inspection or remediation before issuing or renewing a policy |
Reading What You Already Have
The gauge is printed along the outer sheath of the cable, along with the conductor count and whether a ground is included. A marking reading 12/2 WITH GROUND means 12 AWG, two current-carrying conductors plus a bare ground.
Modern non-metallic cable is also color-coded by size, which is a quick check but not a substitute for reading the print. Older cable predates the convention.
| Sheath color | Gauge | Circuit |
|---|---|---|
| White | 14 AWG | 15 A |
| Yellow | 12 AWG | 20 A |
| Orange | 10 AWG | 30 A |
| Black | 8 or 6 AWG | 40–55 A |
| Grey | — | Underground feeder cable (UF), any gauge |
Extension Cords Follow the Same Physics
An extension cord is a wire run, and the same distance and gauge relationship applies, which is why a long thin cord running a space heater gets warm.
| Load | Up to 25 ft | Up to 50 ft | Up to 100 ft |
|---|---|---|---|
| Light duty, under 7 A | 16 AWG | 16 AWG | 14 AWG |
| Medium, 7–10 A | 16 AWG | 14 AWG | 12 AWG |
| Heavy, 10–15 A | 14 AWG | 12 AWG | 10 AWG |
A warm extension cord is undersized for what it is carrying. Space heaters in particular should be plugged directly into a wall outlet. They draw close to a full 15-amp circuit continuously, which is exactly the condition cords are worst at.
Separate Sizing Rules and Cable Types
Metric wire sizes express conductor area in square millimetres (mm²). They do not create a second US code standard. The values below are approximate American Wire Gauge (AWG) conversions used to translate between the two systems.
The NEC sizes an equipment grounding conductor separately from the current-carrying hot conductors. The ground is normally smaller, and its size follows the breaker or fuse rating. The shape of NEC Table 250.122 calls for 14 AWG copper with 15 to 20 amp breakers and 10 AWG with 30 to 60 amp breakers. It then steps up to 8 AWG at 100 amps and 6 AWG at 200 amps. The full table has more rows. Confirm the exact size against the current NEC table or with a licensed electrician because local amendments vary.
Conductors larger than about 4/0 AWG are usually marked in thousand circular mils (kcmil). The 4/0 size is the largest standard AWG size. Larger conductors carry labels such as 250 kcmil, 300 kcmil, and 350 kcmil. A typical single-family service entrance can use this size range between the utility connection or meter and the main panel. Call a licensed electrician for service-entrance or large-feeder sizing.
Nonmetallic sheathed Type B cable (NM-B), commonly known by the Romex trade name, serves most ordinary branch circuits inside dry walls. THHN/THWN is single-conductor wire pulled through metal or polyvinyl chloride (PVC) conduit, often in garages, unfinished basements, and commercial-style wiring. Type THWN carries a wet-location rating. Plain Type THHN does not.
| AWG size | Approximate cross-sectional area |
|---|---|
| 14 AWG | 2.08 mm² |
| 12 AWG | 3.31 mm² |
| 10 AWG | 5.26 mm² |
| 8 AWG | 8.37 mm² |
| 6 AWG | 13.3 mm² |
| 4 AWG | 21.2 mm² |
| 2 AWG | 33.6 mm² |
Romex (NM-B) or THHN
Romex (NM-B) and THHN differ by construction and where the National Electrical Code allows you to install them. NM-B cable bundles two or more insulated conductors with a bare or green ground inside a single non-metallic plastic sheath. You run it directly through bored framing in dry, protected interior walls and ceilings without conduit. THHN is a single insulated conductor without an outer jacket. Because it lacks protective sheathing, code requires you to pull it through metal or PVC conduit. This requirement makes THHN the standard choice for garages, unfinished basements, and exposed runs.
The thermoplastic insulation on both types handles high heat, but only the W in THWN adds a wet-location rating. Plain THHN and NM-B cable are rated strictly for dry locations, and NM-B cannot be buried directly. Conduit gives you long-term flexibility: you can pull new or replacement THHN conductors through existing conduit later, while changing NM-B requires opening finished walls. Neither cable type is inherently safer than the other when installed to code. Choose Romex for standard branch circuits inside dry finished framing, and run THHN through conduit for exposed, damp, or adaptable runs.
| Dimension | Romex (NM-B) | THHN/THWN |
|---|---|---|
| Construction | Factory-assembled cable with ground in a plastic sheath | Single insulated conductor without outer jacket |
| Where it is used | Concealed interior wall and ceiling framing | Garages, unfinished basements, and exposed runs |
| Conduit requirement | None (run directly through framing) | Required (pulled through metal or PVC conduit) |
| Moisture rating | Dry, protected interior locations only | Wet or damp locations for THWN (plain THHN is dry only) |
| Typical use case | Standard residential interior branch circuits | Exposed runs and locations subject to moisture or damage |
Common questions
What size wire do I need for a 20 amp circuit?
12 AWG copper as a minimum. 14 AWG is rated for 15 amps only, and pairing it with a 20-amp breaker means the cable can overheat before the breaker ever trips.
Can I use 12 gauge wire on a 15 amp circuit?
Yes. Oversizing the conductor is always permitted. The breaker protects the wire, so a heavier wire is simply better protected. It also leaves the option of upgrading to a 20-amp circuit later.
Does wire gauge get bigger or smaller as the number goes up?
Smaller. AWG runs inversely: 14 AWG is thinner than 12, which is thinner than 10, and roughly every three gauge steps down doubles the cross-sectional area.
What gauge wire for a 100 foot run?
Usually one size larger than the chart suggests, because of voltage drop. A 20-amp circuit that would normally use 12 AWG typically wants 10 AWG at 100 feet to stay within a 3 percent drop.
Is aluminum wiring safe?
Aluminum is fine and standard for large feeders. Aluminum branch wiring in homes from roughly 1965 to 1973 is the concern. It loosens at terminations and has a documented fire association. It needs CO/ALR-rated devices or approved copper pigtails, fitted by an electrician.
Is aluminum wiring dangerous?
Aluminum branch wiring from homes built roughly between 1965 and 1973 is a real concern because aluminum expands and contracts more than copper through heating and cooling cycles. That movement loosens connections at outlets and switches over time, and a loose connection arcs and overheats. Aluminum used in large feeders and service entrance conductors is not the same concern.
How do you fix aluminum wiring without rewiring the whole house?
A licensed electrician can remediate aluminum branch circuits without a full rewire in two accepted ways: pigtailing a short length of copper wire onto the aluminum conductor with an approved CO/ALR-rated connector so the device wires to copper, or replacing switches and outlets with devices rated CO/ALR for direct connection to aluminum.