What Size Wire for 20 Amps? — Complete NEC Guide
For a 20 amp circuit, you need 12 AWG copper wire or 10 AWG aluminum wire per NEC Table 310.16. Use a 20A breaker. Here is the complete sizing guide with distances, costs, and professional tips.
Common Uses for 20 Amp Circuits
Kitchen countertop outlets (SABC), bathroom GFCI outlets, garage outlets, laundry room outlets, outdoor outlets. These applications require a dedicated 20A breaker and 12 AWG copper wire (or 10 AWG aluminum for longer runs or cost savings).
The wire size is determined by NEC Table 310.16, which lists the maximum allowable ampacity for each conductor size based on insulation temperature rating and conductor material. For 20 amps, the minimum conductor size at 75°C insulation (the most common rating for modern wire) is 12 AWG for copper and 10 AWG for aluminum.
Maximum Wire Run Distance
Wire gauge determines not just ampacity but also voltage drop over distance. For a 20 amp load:
At 240V: 100 ft with 12 AWG. At 120V: 50 ft with 12 AWG.
If your wire run exceeds these distances, you must upsize the wire by one or two gauges to keep voltage drop under the NEC-recommended 3% for branch circuits. Use our Voltage Drop Calculator to check your specific run.
NEC Code Reference
The 20 amp wire size requirement comes from NEC 210.11(C), Table 310.16. This table provides ampacity ratings for insulated conductors rated 0 through 2000 volts, 60°C through 90°C, not more than three current-carrying conductors in raceway, cable, or earth. For ambient temperatures above 30°C (86°F), derating factors from NEC Table 310.15(B)(1) must be applied.
Kitchen Small Appliance Circuits
NEC 210.11(C)(1) requires at least two 20A small appliance branch circuits serving kitchen countertop receptacles. These circuits cannot serve any other outlets or lighting — they are dedicated to countertop use only.
Conduit vs. Romex Installation
For residential work, NM-B (Romex) 12/2 with ground is the standard choice for concealed wiring in walls and attics. For exposed runs in garages, basements, or outdoors, use THHN 12 AWG in EMT or PVC conduit. In commercial and industrial settings, individual THHN 12 AWG conductors in conduit are standard.
When running in conduit with more than 3 current-carrying conductors, ampacity must be derated per NEC 310.15(C). This means the effective ampacity of 12 AWG may be less than 20A, requiring you to upsize. Use our Derating Calculator to check.
Wire Cost Estimate
12 AWG copper wire costs approximately $0.25-0.40 per foot for NM-B (Romex) cable. For a typical 50-foot run, expect to spend $25-90 on wire alone, plus breaker ($5-15), box, connectors, and labor if hiring an electrician. Aluminum wire costs roughly 40-60% less than copper for equivalent ampacity but requires larger gauge sizes.