WireGaugeCalc Free calculator · NEC cited · works offline
House Circuit Breaker Calcualtor
House circuit breaker calcualtor is quick with WireGaugeCalc, which returns the breaker amperage that fits a circuit load and conductor size.
Enter the circuit load and the conductor you plan to run, and the tool returns the matching overcurrent device rating.
You get a breaker size that protects the wire, so the circuit stays inside its ampacity.
Open the calculatorEnter any two values and read the rest.
Ohm’s law: V = I × R and P = V × I. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Match the Breaker to the Conductor
A breaker protects the conductor, so its rating must not exceed the ampacity of the wire it feeds.
The tool checks the load against the conductor, since a 15 amp circuit on 14 AWG and a 20 amp circuit on 12 AWG follow set pairings.
Continuous loads are figured at 125 percent, so the calculator helps you avoid a breaker that nuisance trips.
What the Breaker Result Considers
The breaker size comes from how the load and wire line up:
- Total circuit load in amps or watts
- Conductor size and its ampacity
- Copper or aluminum conductor
- Continuous versus non-continuous load
- Standard breaker ratings such as 15, 20, 30, and 40 amps
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 put a 20 amp breaker on 14 AWG wire?
No. 14 AWG copper is limited to a 15 amp breaker, since a 20 amp device would not protect the conductor. Use 12 AWG copper for a 20 amp circuit, and verify against the current NEC and your local authority having jurisdiction.
How does a continuous load change the breaker size?
A continuous load is sized at 125 percent, so a breaker and conductors must carry that higher figure. The calculator applies the multiplier when you mark a load as continuous.
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.