WireGaugeCalc Free calculator · NEC cited · works offline
Maximum Fill For Conduit
Maximum fill for conduit is quick with WireGaugeCalc, which applies the NEC percent limit and shows how many conductors fit.
It uses the conduit and wire areas from NEC Chapter 9, so the math is done for you.
Set the size and wires and read the result against the allowable area.
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.
Applying The Right Percent Fill Limit
The calculator picks the correct limit, since one wire allows 53 percent, two allow 31 percent, and three or more allow 40 percent.
It compares total conductor area to the conduit area, so you see whether the EMT or PVC run is within range.
It flags an overfilled raceway before you pull the wire.
What Sets The Allowable Conduit Area
The maximum fill depends on a short list of inputs:
- Conduit type, EMT, PVC, or RMC
- Trade size of the raceway
- Number of conductors in the run
- Wire gauge and insulation
- Whether grounds are included
- Total cross-section area versus the limit
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 is the maximum fill percentage for three or more wires?
For three or more conductors, the maximum fill is 40 percent of the conduit cross-section. Always check this against the current NEC Chapter 9 and your local authority having jurisdiction.
Why is a single conductor allowed 53 percent fill?
A single conductor allows 53 percent because there is more room to pull without binding. The limit drops to 31 percent for two wires and 40 percent for three or more.
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.