WireGaugeCalc Free calculator · NEC cited · works offline
NEC Wire Size Calculator
nec wire size calculator is fast with WireGaugeCalc.
You enter the load, conductor material, and termination temperature, and the tool returns a conductor size that satisfies NEC 310.16 ampacity.
So you can size the run with the same logic an inspector applies.
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.
Sizing Conductors To NEC 310.16
The tool starts from your amperage and reads the smallest conductor that carries it in the 60, 75, or 90 degree C column.
Since termination ratings cap the usable column, the result respects the lowest rated lug or breaker in the circuit.
Copper and aluminum give different sizes for the same load, so the calculator keeps the material you selected throughout.
Inputs The Calculator Uses
Each field shapes the conductor size you get:
- Load in amps or the connected wattage and voltage
- Conductor material, copper or aluminum
- Termination temperature, 60, 75, or 90 degree C
- Number of current-carrying conductors for derating
- The resulting AWG or kcmil size
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
Does this calculator use NEC 310.16 ampacity?
Yes, it reads allowable ampacity from the 310.16 table and applies the termination column you choose. Verify the final size against the current NEC and your local authority having jurisdiction.
Why does termination temperature matter for sizing?
Most breakers and lugs are listed at 75 degree C, so the conductor is sized from that column even if the insulation is rated 90 degree C. Using the lower column keeps the connection within its listing.
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.