WireGaugeCalc Free calculator · NEC cited · works offline
What Size Wire For 20 Amp Circuit
what size wire for 20 amp circuit is simple with WireGaugeCalc, since you enter 20 amps and the calculator returns the conductor that carries it.
The tool reads NEC 310.16 ampacity for copper or aluminum at your termination temperature, so the gauge it shows actually matches the breaker.
You confirm the right wire in one step, so the circuit is protected and the conductor never runs past its rating.
Open the calculatorSmallest conductor whose ampacity meets the load, NEC Table 310.16. Field aid only, verify against the current NEC and your local authority having jurisdiction.
How the 20 amp breaker wire size is set
A 20 amp breaker protects a conductor rated for at least 20 amps, so the wire and the breaker have to match.
Copper 12 AWG carries 20 amps in the 60 degree C column, so it is the common 20 amp breaker wire size for general copper branch circuits.
WireGaugeCalc shows the gauge for your material, so you avoid pairing a heavy breaker with an undersized wire.
What size wire for 20 amp breaker on longer runs
The base answer can change once a few factors come into play:
- Copper typically uses 12 AWG for 20 amps
- Aluminum needs a larger gauge for the same load
- Long runs may upsize to hold voltage drop near 3 percent
- More than three current-carrying conductors triggers derating
- High ambient temperature reduces allowable ampacity
- Termination temperature sets which 310.16 column applies
One app for every NEC calculation
WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
Can I use 14 gauge wire on a 20 amp breaker?
No. 14 AWG copper is rated 15 amps, so a 20 amp breaker would let current run past the wire's rating before it trips. Use 12 AWG copper for a 20 amp circuit.
Is the 20 amp breaker size wire different for a long kitchen run?
It can be. The ampacity answer stays 12 AWG copper, but a long run may push voltage drop too high, so you upsize to 10 AWG to keep the drop reasonable. Verify the final size against the current NEC and your local authority having jurisdiction.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.