WireGaugeCalc Free calculator · NEC cited · works offline
Subpanell Fill Calculation
Subpanell fill calculation is quick with WireGaugeCalc, since you enter the feeder conductors and the calculator checks them against the conduit fill limit.
It uses NEC Chapter 9 areas for EMT, PVC, or RMC and applies the 40% fill rule, so the feeder raceway to your subpanel is not overstuffed.
You get the minimum conduit size that carries the feeder set within code.
Open the calculatorFill against NEC Chapter 9, Table 1 (40% for 3+ conductors) with Table 4 and Table 5 areas. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Size The Feeder Conduit For A Subpanel
The calculator sums the area of the hots, neutral, and grounding conductor, then compares it to the conduit area, since three or more wires cap fill at 40%.
It runs the numbers for EMT, PVC, or RMC, so you can pick the raceway that fits the feeder run and the wall path.
Inputs Behind The Subpanel Feeder Fill
The feeder conduit size depends on these factors:
- Number and size of feeder phase conductors
- Neutral and equipment grounding conductor
- Conduit type: EMT, PVC, or RMC
- NEC Chapter 9 conductor and raceway areas
- The 40% fill limit for the full feeder set
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
Do I count the neutral and ground in a subpanel feeder?
Yes, the neutral and the equipment grounding conductor both count toward conduit fill. The calculator adds every conductor in the raceway when sizing the feeder conduit.
Why is the feeder conduit capped at 40% fill?
The 40% limit leaves room to pull conductors and to dissipate heat in the raceway. Confirm the trade size against 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.