WireGaugeCalc Free calculator · NEC cited · works offline
Size Wire Needed To Run 100 Amps 125 Ft
size wire needed to run 100 amps 125 ft is fast with WireGaugeCalc, since you enter the amps, run length, and material and the tool returns the gauge.
The calculator checks NEC 310.16 ampacity first, then verifies the conductor against voltage drop over the 125 foot run.
You get a gauge that carries the load and stays within the drop guideline.
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.
Ampacity And Voltage Drop Over A 125 Ft Run
At 100 amps the conductor must first meet the 75C ampacity column, so the base gauge comes from NEC 310.16.
Because 125 feet is a long run, the calculator may upsize the conductor to hold voltage drop near the 3 percent branch-circuit guideline.
Copper and aluminum reach that target at different gauges, so the tool reports each material separately.
How The Tool Sizes A 100 Amp Run
Give the calculator the run details:
- Load of 100 amps
- One-way run length of 125 ft
- Conductor material, copper or aluminum
- System voltage, such as 120 or 240
- Termination temperature for ampacity
- Result as the gauge that meets ampacity and voltage drop
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
Does 125 ft mean I need to upsize past the ampacity gauge?
It can. The ampacity gauge for 100 amps may still drop more than 3 percent over 125 ft, so the calculator increases the conductor when the drop is too high.
Is the 3 percent voltage drop limit a code requirement?
No, 3 percent on a branch circuit is an NEC recommendation in an informational note, not a mandatory rule. Treat it as a target and confirm any requirement with 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.