WireGaugeCalc Free calculator · NEC cited · works offline
Branch Circuit Calculator
branch circuit calculator is simple with WireGaugeCalc.
You enter the connected load, voltage, and run length, and the tool returns the conductor size, the breaker that fits, and the voltage drop on the run.
So you can lay out the circuit with honest numbers from the start.
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.
Working The Branch Circuit Math
The tool applies Ohm's law and the load rules to turn watts and volts into the amperage the circuit draws.
Since the conductor must carry that current, it reads the size from the ampacity table and checks the breaker rating against it.
It then estimates voltage drop so a long run does not quietly underfeed the load.
What The Calculator Returns
From a few inputs you get:
- The branch circuit load in amps
- A conductor size that carries the current
- The matching overcurrent device rating
- Voltage drop over the run length
- A note when the load nears the circuit limit
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
How much can I load a branch circuit?
Continuous loads are generally limited to 80 percent of the circuit rating, so a 20 amp circuit carries about 16 amps continuously. Check the load type and the current NEC with your local authority having jurisdiction.
Does the calculator size the breaker too?
It reports an overcurrent device rating that matches the conductor and load you entered. Always confirm the device against the equipment listing and the NEC for your install.
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.