WireGaugeCalc Free calculator · NEC cited · works offline
100 Amp Wire Size Calculator
100 amp wire size calculator is fast with WireGaugeCalc, since you enter the amps, the material, and the termination temperature.
It compares the load to the NEC 310.16 ampacity table so the conductor carries 100 amps safely.
You get the copper or aluminum gauge in one step, so you can pull the feeder.
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 100 Amps with the NEC Wire Sizing Calculator
The NEC wire sizing calculator reads the 310.16 table at your termination temperature, so the column matters as much as the amps.
Copper at 75C reaches 100 amps at 3 AWG, while aluminum needs 1 AWG, since aluminum carries less current per size.
It checks both materials so you can compare cost and pull difficulty.
Inputs for the 100 Amp Wire Size
Set these and the calculator returns the gauge:
- 100 amp circuit rating
- Copper or aluminum conductor
- Termination temperature column
- Run length for voltage drop
- Ambient temperature, if derating applies
- Number of current-carrying conductors
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 is needed for 100 amps?
At the 75C column, 3 AWG copper carries 100 amps. For a feeder or dwelling service, an allowance may permit a different size, so check the conditions for your run.
Can I use aluminum for a 100 amp feeder?
Yes, aluminum is common for feeders, and 1 AWG aluminum reaches 100 amps at 75C. Confirm the conductor and termination listing against the current NEC and your local authority having jurisdiction.
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.