WireGaugeCalc Free calculator · NEC cited · works offline
Nec Wire Size
nec wire size is simple to read with WireGaugeCalc, since the app maps your load to the 310.16 ampacity table.
You enter amps, conductor material, and the termination temperature, so the calculator returns the conductor the code allows.
That gives you a number you can defend at inspection.
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 NEC Wire Sizing Works
The 310.16 table lists ampacity by gauge across the 60, 75, and 90 degree C columns, so the conductor must meet the load in the right column.
Termination temperature usually limits the answer, since most breakers and lugs are rated for 75 degrees C.
Copper carries more current than aluminum, so the calculator shows both materials for the same load.
Inputs That Drive NEC Wire Sizing
The calculator weighs these factors for a code-compliant result:
- Load in amps, the starting point for the lookup
- Conductor material, copper or aluminum
- Termination temperature column, 60, 75, or 90 degrees C
- Continuous load, multiplied by 125 percent
- 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
Which temperature column does NEC wire sizing use?
You size by the load, but you cannot exceed the rating of the lowest rated terminal, which is often the 75 degree C column. Confirm the terminal rating and the current NEC with your local authority having jurisdiction.
Why does aluminum need a larger gauge than copper?
Aluminum has higher resistance, so it carries less current per gauge and needs a larger conductor for the same load. The calculator lists the copper and aluminum choices together.
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.