WireGaugeCalc Free calculator · NEC cited · works offline
Circuit Ampacity Calculator
Circuit ampacity calculator is quick with WireGaugeCalc, since you choose the wire size, material, and temperature column and it returns the ampacity.
It pulls values straight from NEC 310.16 so the rated current matches the table.
You confirm the conductor can carry the load before you connect it.
Open the calculatorAllowable ampacity from NEC Table 310.16 at the chosen termination temperature. Field aid only, verify against the current NEC and your local authority having jurisdiction.
An ampacity calculator that respects the termination column
The tool lets you pick the 60, 75, or 90 degree C column, since terminations limit the usable ampacity.
It separates copper from aluminum because the two metals carry different current at the same size.
Reading the right column keeps the breaker and the wire matched.
Check copper and aluminum the same way
This copper wire ampacity calculator handles both materials across NEC 310.16:
- Copper and aluminum conductors
- 60, 75, and 90 degree C termination columns
- Sizes from 14 AWG through large kcmil
- Rated ampacity straight from the table
- Note when the 90 column is for derating only
- Clear material and column labels
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 should I use?
Use the column that matches the lowest rated termination on the circuit, often 75 degrees C for breakers and lugs. The 90 degree C column is generally for derating, not for the final connection. Confirm with the current NEC and your local authority having jurisdiction.
Why is aluminum rated lower than copper?
Aluminum has higher resistance than copper, so a given size carries less current. This ampacity calculator shows the correct value for whichever metal you select.
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.