Electrical Wire Sizes: 12/2 vs 14/2, 20 Amp and THHN
A 20 amp household circuit takes 12 AWG copper wire and a 15 amp circuit takes 14 AWG; in 12/2 the 12 is the gauge and the 2 is the number of insulated wires.
By Andrian ChengContributing writer.
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The short answer
For copper house wire, the wire maker Cerrowire pairs each gauge with a circuit size:
| Wire gauge (copper) | Circuit rating | Typical uses in Cerrowire's chart |
|---|---|---|
| 14 AWG | 15 amps | Lighting fixtures, lighted medicine cabinets |
| 12 AWG | 20 amps | Receptacles, dishwashers, disposals, room air conditioners |
| 10 AWG | 30 amps | Electric dryers, single ovens, large air conditioners |
| 8 AWG | 40 amps | Larger appliance circuits |
| 6 AWG | 55 amps | Built-in double ovens, double oven ranges |
The smaller the gauge number, the thicker the wire. Southwire's spec sheet gives a solid copper diameter of 0.064 inch for 14 AWG, 0.080 inch for 12 AWG and 0.101 inch for 10 AWG.
What size wire for a 20 amp circuit
Use 12 AWG copper. The wire must match the breaker: 12 AWG on a 20 amp breaker, 14 AWG on 15 amps. Putting 14 AWG on a 20 amp breaker lets more current through the wire than it is rated for, and Cerrowire warns that overloaded circuits can overheat the wire.
You may see higher numbers for the same gauge. Southwire lists 12 AWG THHN at 25 amps at 75°C and 30 amps at 90°C in a raceway. Those figures describe the bare conductor's ampacity, not the breaker you put on a house circuit. Follow the circuit chart, check your local code, and hire a licensed electrician when in doubt.
12/2 vs 14/2 wire
Cable labels read gauge first, then the number of insulated wires:
- 14/2 with ground: two insulated 14 AWG wires plus a bare ground. For 15 amp circuits.
- 12/2 with ground: two insulated 12 AWG wires plus a ground. For 20 amp circuits.
- 12/3 with ground: three insulated wires plus a ground. Cerrowire lists it for 3-way light switches.
Inside homes the usual cable is NM-B, a jacket with several wires inside. Cerrowire describes it as primarily for residential branch circuits in dry locations, with ampacity limited to the 60°C rating. For outdoor and buried runs, its chart switches to UF-B in the same gauges.
What does THHN mean
THHN is a single insulated wire, sold one conductor at a time and pulled through conduit. The letters describe how it is built:
- T: thermoplastic insulation (PVC).
- HH: high heat rating. Southwire rates THHN for dry locations up to 90°C.
- N: a nylon outer jacket.
Cerrowire explains that the nylon adds resistance to gasoline and oil and protects the PVC from scuffs during installation, but it is not the electrical insulation. THHN is often sold dual rated as THWN, as Southwire's is; Southwire allows THWN in wet locations up to 75°C. Both are rated 600 volts.
Also note that the wires inside NM-B cable may look like THHN, but Cerrowire notes they are not marked or rated as THHN and cannot be stripped out of the cable for use in conduit.
Shopping for wire
The 97 electrical wire listings in tools and home improvement on Wiki Shopping on October 26, 2026 lean toward small hookup and low-voltage wire: 13 list 18 AWG, 11 list 22 AWG, 8 list 14 AWG and 7 list 16 AWG. For house circuits, check that the listing names the cable type, such as NM-B or THHN, as well as the gauge.
How we count
Gauge counts are read from each store listing on Wiki Shopping. Listings that do not state a gauge are left out, and the counts change as listings are added or removed.