WireGaugeCalc Free calculator · NEC cited · works offline
2-20 Amp Breaker Wire Size
2-20 amp breaker wire size is simple to confirm with WireGaugeCalc, since the tool reads the breaker rating, material, and run and returns the conductor.
You enter 20 amps, pick copper or aluminum, and set the run, so the calculator gives the AWG that matches the NEC 310.16 ampacity.
That keeps each 20 amp circuit on the right wire.
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.
Why 20 Amp Breakers Almost Always Land On 12 AWG Copper
A 20 amp breaker protects the conductor, so the wire must carry at least 20 amps at the termination temperature.
12 AWG copper is rated 20 amps in the 60 and 75 degree C columns, so it is the standard match for a 20 amp breaker.
The calculator confirms the AWG and flags when a long run forces an upsize for voltage drop.
What Sets The Conductor For Two 20 Amp Circuits
Each 20 amp circuit is sized from these inputs:
- The 20 amp breaker rating per circuit
- Copper or aluminum conductor
- The 60 or 75 degree C termination column
- Run length, since long runs add voltage drop
- Ambient temperature and conductor count for derating
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 on a 20 amp breaker?
No, 14 AWG copper is rated 15 amps, so a 20 amp breaker would not protect it. Use 12 AWG copper for a 20 amp circuit, and confirm the choice against the current NEC and your local authority having jurisdiction.
Do two 20 amp circuits need separate wire size checks?
Each circuit is sized for its own 20 amp load, so the base conductor is the same. If both share a conduit you may also need to derate for conductor count.
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.