WireGaugeCalc Free calculator · NEC cited · works offline
125 Amp Panel Wire Size
125 amp panel wire size is quick to set with WireGaugeCalc, since you enter the amperage and it returns the conductor the NEC allows for the feeder.
The calculator reads NEC 310.16, so it matches the gauge to copper or aluminum and to the 75 degree C terminations on the panel.
You get the feeder size in seconds, so a 125 amp panel is sized without guessing at the table.
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 the Feeder Conductor
The calculator picks a conductor whose ampacity meets or beats 125 amps, since the feeder must carry the panel's rating.
It compares copper and aluminum at the same amperage, so you can see how the metal changes the gauge you need.
Every result is tied to the termination column the lugs use, so the rating you read is the one that applies.
What WireGaugeCalc Checks for a 125 Amp Feeder
The tool walks the same path you would check by hand:
- Reads ampacity from NEC 310.16 for your conductor
- Confirms the rating meets the 125 amp panel load
- Switches between copper and aluminum sizes
- Holds to the 75 degree C termination column
- Notes when conduit conditions call 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
What size copper wire feeds a 125 amp panel?
A 125 amp feeder usually uses 1 AWG copper at the 75 degree C column, since that gauge carries 130 amps. Verify the size against the current NEC and your local authority having jurisdiction, since derating or conduit conditions can change it.
What aluminum size works for a 125 amp panel?
Aluminum needs a larger gauge than copper, so a 125 amp feeder often uses 2/0 aluminum. The calculator shows both metals so you can compare the gauges directly.
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.