WireGaugeCalc Free calculator · NEC cited · works offline
100 Amp Service Wire Size
100 amp service wire size is simple to find with WireGaugeCalc, since the app reads the NEC 310.16 ampacity table for your conductor and temperature.
You pick copper or aluminum and the termination temperature column, then the app returns the gauge that carries 100 amps.
You get the conductor size in seconds, so you can size the service entrance with the table behind every result.
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 calculator reads NEC 310.16 for a 100 amp service
Ampacity rises with conductor size, so the app finds the smallest gauge that meets or beats 100 amps in your chosen column.
Copper carries more current than aluminum at the same gauge, so switching material changes the result.
Most lugs are rated 75 degrees C, so the app uses that column unless you tell it otherwise.
What sets the conductor size for a 100 amp service
A few inputs decide the gauge:
- Conductor material, copper or aluminum
- Termination temperature rating, 60, 75, or 90 degrees C
- The 100 amp service rating itself
- Whether the run is service entrance or a feeder
- Any ambient or bundling adjustments that apply
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 copper wire is used for a 100 amp service?
At the 75 degree C column, 3 AWG copper carries 100 amps, and 4 AWG copper is common where the dwelling service rule allows it. Confirm the gauge against the current NEC and your local authority having jurisdiction.
What aluminum size works for a 100 amp service?
Aluminum needs more area than copper, so 1 AWG aluminum at 75 degrees C is the usual pick, with 2 AWG allowed under the residential service feeder rule. Verify against the NEC table and your inspector.
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.