WireGaugeCalc Free calculator · NEC cited · works offline
Main To Electrical Panel Wire Size
Main to electrical panel wire size is fast with WireGaugeCalc, which sizes the feeder from your service amperage, conductor material, and the breaker termination temperature.
It reads the NEC 310.16 ampacity tables for you, so you do not flip pages to match amps to a conductor.
Enter the values once and you get the copper or aluminum size that carries the load to the panel.
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 For Your Service Amps
The calculator matches your service amperage to an ampacity in NEC 310.16, since the conductor must carry the full load without overheating.
It lets you pick the 60, 75, or 90 degree column, as the termination rating on the breaker and lugs sets which value applies.
It compares copper and aluminum so you can see the larger aluminum size needed for the same amps.
What Drives The Conductor Size To The Panel
A few inputs decide the gauge for a main feeder run:
- Service amperage, such as 100, 150, or 200 amps
- Conductor material, copper or aluminum
- Termination temperature, usually the 75 degree column
- Whether the conductors are in conduit or a cable assembly
- Ambient temperature if the run is hot
- Number of current-carrying conductors in the raceway
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 wire feeds a 200 amp panel?
At the 75 degree column, 200 amps commonly uses 2/0 copper or 4/0 aluminum. Confirm the value against the current NEC tables and your local authority having jurisdiction before you pull conductors.
Does the breaker termination rating change the wire size?
Yes, since most breakers and lugs are rated at 75 degrees, you size to that column even if the cable is rated higher. Using a hotter column without rated terminations can undersize the feeder.
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.