WireGaugeCalc Free calculator · NEC cited · works offline
NEC Conduit Fill
NEC conduit fill is fast with WireGaugeCalc, since the calculator takes your conductor sizes and counts and returns the fill percentage against the allowed limit.
You pick the raceway type and trade size, enter each conductor, and the math follows NEC Chapter 9 tables for cross-sectional area.
So you can size the raceway right the first time and avoid pulling wire that overfills the conduit.
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.
How Conduit Wire Fill Works
The code caps three or more conductors at 40% fill, so the calculator sums each conductor area and compares it to the inside area of the conduit.
Since one conductor is allowed 53% and two conductors are allowed 31%, the tool applies the right limit for your conductor count automatically.
What Drives EMT, PVC, and RMC Fill
A few inputs decide whether your conductors fit the raceway:
- Raceway type, since EMT, PVC, and RMC each have different inside areas per trade size
- Conductor insulation, as THHN and XHHW have different cross-sectional areas
- Conductor count, which sets the 53%, 31%, or 40% fill limit
- Trade size of the conduit, from 1/2 inch up
- Mix of conductor sizes in the same run
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 NEC conduit fill for four wires?
With three or more conductors the limit is 40% fill. The calculator adds the area of all four conductors and checks it against 40% of the conduit inside area.
Do EMT and PVC have the same fill capacity?
No, since their inside diameters differ by trade size, so the same conductors can fit one and overfill the other. Always confirm the raceway type, and verify the result 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.