WireGaugeCalc Free calculator · NEC cited · works offline
100 Amp Wire Size
100 amp wire size is simple with WireGaugeCalc, since you pick the material and it returns the conductor that meets the load.
The tool reads NEC 310.16 and the termination column you set, so the gauge matches how a 100 amp breaker and lug are rated.
You confirm the conductor for a 100 amp feeder or service before you order wire.
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.
What Size Wire for 100 Amp on Copper and Aluminum
At the 75 degree C column, 3 AWG copper carries 100 amps, so copper feeders often land there.
Aluminum has lower ampacity, so the size wire for 100 amp steps up to 1 AWG at the same column.
Since the termination rating sets the limit, the tool holds you to the column the equipment is listed for.
How the 100a Wire Size Result Is Built
Enter the circuit and the wire size for 100 amp answer comes from these inputs:
- Copper or aluminum conductor choice
- 60, 75, or 90 degree C termination column
- NEC 310.16 ampacity at 100 amps
- Standard AWG and kcmil sizes
- Service or feeder application note
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 for 100 amp service feeder?
At the 75 degree C column, 3 AWG copper or 1 AWG aluminum carries 100 amps. NEC 310.12 also allows reduced sizes for some dwelling services, so check whether that rule applies. Confirm against the current NEC and your local authority having jurisdiction.
Can I use 4 AWG copper for a 100 amp circuit?
4 AWG copper is rated 85 amps at 75 degrees C, so it falls short of a full 100 amp load. Use 3 AWG copper unless a dwelling service reduction applies.
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.