WireGaugeCalc Free calculator · NEC cited · works offline
What Size Wire For 100 Amp Service
What size wire for 100 amp service is simple to settle with WireGaugeCalc, since the calculator applies the NEC service conductor rules for you.
You enter copper or aluminum and the calculator returns the minimum gauge that carries the 100 amp rating safely.
You see the answer right away, so you can size the service and the run before you order cable.
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.
Minimum Gauge Wire For 100 Amp Service
The wire size for 100 amp service is commonly 4 AWG copper or 2 AWG aluminum, since the dwelling service rule lets a 100 amp service use those reduced conductors.
Aluminum runs larger, so the calculator separates the two materials and shows each result.
The tool checks the value against the table, so the service wire rating for the 100 amp main breaker is clear.
What Size Wire Do I Need For 100 Amp Service
The result depends on a few service inputs:
- Conductor material, since copper and aluminum carry different current per gauge
- Whether the dwelling service rule applies, as it allows a smaller conductor
- The 100 amp main breaker rating the conductor must support
- Termination temperature at the panel lugs, usually 75 degrees C
- Run length, since a long service may need an upsize for voltage drop
- The size of cable for 100 amp service listed in the NEC tables
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
Is 4 AWG copper enough for a 100 amp service?
For a dwelling service, the rule allows 4 AWG copper or 2 AWG aluminum at 100 amps under the reduced sizing provision. For a feeder that is not a dwelling service, use 3 AWG copper instead.
What size aluminum wire for 100 amp service?
A 100 amp dwelling service commonly uses 2 AWG aluminum, or 1 AWG aluminum for a standard feeder. Confirm the exact size against the current NEC and your local authority having jurisdiction.
Does the run length change the service wire size?
A long service run can require an upsize so voltage drop stays reasonable. The calculator can flag this when you add the distance.
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.