WireGaugeCalc Free calculator · NEC cited · works offline
Calculate Current Rating Cable
Calculate current rating cable values fast with WireGaugeCalc, which reads the NEC 310.16 ampacity for a given conductor size and type.
You enter the wire gauge, copper or aluminum, and the termination temperature, and the tool returns the allowable ampacity.
So you know the cable carries the load before you connect it to the 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 The Current Carrying Capacity Calculator Reads Ampacity
Cable ampacity comes from NEC Table 310.16, since that table lists the allowable current for each conductor size by insulation rating.
Copper carries more current than aluminum at the same gauge, so the material choice changes the rating directly.
The current carrying capacity calculator pulls the correct column so the rating matches the conductor you are using.
What Sets A Cable's Current Rating
Several factors decide the allowable current:
- Conductor size, since larger wire carries more amps
- Material, because copper rates higher than aluminum per gauge
- Termination temperature, which limits you to the 60, 75, or 90 degree column
- Ambient temperature, which can require a derating factor
- Number of current-carrying conductors bundled together
- Insulation type, as THHN and XHHW use different columns
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 for the cable rating?
Use the column that matches the lowest rated termination on the circuit, often 75 degrees C for most breakers and lugs. Confirm the column against the current NEC 110.14 and your local authority having jurisdiction.
Why does the calculator ask for copper or aluminum?
Aluminum has lower ampacity than copper at the same gauge, so NEC Table 310.16 lists separate values. Choosing the wrong material would oversize or undersize the cable.
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.