WireGaugeCalc Free calculator · NEC cited · works offline
Sub Panel Load Calculator
Sub panel load calculator is fast with WireGaugeCalc, since you enter the loads and the tool returns the feeder size.
The calculator totals the sub panel demand and matches it to a conductor using NEC 310.16 ampacity.
You get the feeder gage and breaker before you pull wire to the remote panel.
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.
Panel Sizing Calculator For The Feeder Run
A sub panel feeder must carry the calculated demand, so undersizing the conductor trips the breaker or overheats the run.
WireGaugeCalc sets the feeder gage from 310.16, with the conductor material and the termination temperature column in view.
It checks the breaker against the conductor so the overcurrent device protects the wire.
What The Sub Panel Feeder Size Depends On
The feeder conductor comes from a few values:
- The total calculated demand feeding the sub panel
- Copper or aluminum conductor material
- The 60, 75, or 90 degree termination column
- The NEC 310.16 ampacity for that gage
- The breaker rating that protects the feeder
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 wire feeds a 100 amp sub panel?
A 100 amp feeder is often 3 AWG copper or 1 AWG aluminum at the 75 degree column, but length and conditions can change it. Run your numbers in WireGaugeCalc and verify against the current NEC and your local authority having jurisdiction.
Does the sub panel feeder need a separate ground?
Yes, a feeder to a remote sub panel uses four wires with an equipment grounding conductor and isolated neutral. The calculator sizes the feeder phase conductors so you can match the ground to it.
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.