WireGaugeCalc Free calculator · NEC cited · works offline
NEC Wire Sizes Based On Breakers Size Or Load
NEC wire sizes based on breakers size or load are simple with WireGaugeCalc, since the calculator is embedded on this page.
You enter the breaker amps or the calculated load, pick copper or aluminum, and choose the termination temperature column.
That means you get the minimum AWG that matches the overcurrent device without flipping through the NEC 310.16 table.
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.
Matching the breaker to the conductor ampacity
A conductor must carry the load and be protected by the breaker, so its ampacity has to meet or exceed the breaker rating.
WireGaugeCalc reads NEC 310.16 and returns the smallest wire that fits the amps you enter.
It checks both the breaker size and the load current, so you can size from whichever number drives the circuit.
Termination temperature and conductor material
The result depends on a few choices you make:
- Breaker or load current in amps
- Copper or aluminum conductor
- 60C, 75C, or 90C termination column
- Continuous load, which adds the 125% factor
- Wire size returned in AWG or kcmil
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
Which termination temperature column should I use?
Most equipment and breakers are rated for 75C terminations at typical sizes, so the 75C column is common. Always confirm the actual termination rating on the device and verify against the current NEC and your local authority having jurisdiction.
Do I size wire from the breaker or from the load?
The conductor ampacity must be high enough for the load and be protected by the breaker. The calculator lets you check both numbers so the larger one controls the size.
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.