WireGaugeCalc Free calculator · NEC cited · works offline
Elecrical Wire Size Amp Rating
Elecrical wire size amp rating is simple with WireGaugeCalc, since you enter the load and material and the app returns the matching conductor gauge.
The calculator reads NEC 310.16 ampacity, so the size is tied to the copper or aluminum rating and the termination temperature column.
You get the correct gauge for the amps before you cut wire, so the circuit lands on the right breaker.
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 Ampacity Sets The Gauge
Each conductor has an amp rating in NEC 310.16, so the gauge must carry the circuit load with margin.
WireGaugeCalc reads the 60C, 75C, or 90C column based on your termination temperature.
Since copper carries more than aluminum per size, the app shows both so you match the wire to the breaker.
Matching Conductor Size To The Load
The calculator works from the values that set the rating:
- Circuit load in amps
- Copper or aluminum conductor material
- Termination temperature column from NEC 310.16
- 60C, 75C, or 90C ampacity selection
- Recommended gauge for the breaker 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
What amp rating does 12 AWG copper carry?
12 AWG copper is rated 25 amps at 90C but is commonly protected at 20 amps for general branch circuits. Verify the rating and overcurrent limit against the current NEC and your local authority having jurisdiction.
Why does termination temperature change the size?
Most lugs and breakers are rated 75C, so even a 90C wire is sized from the 75C column, and the calculator reads the column that matches your equipment.
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.