WireGaugeCalc Free calculator · NEC cited · works offline
Conduit Size Calculator
Conduit size calculator is quick with WireGaugeCalc, since you list your conductors and the tool finds the smallest raceway that fits.
It compares the total conductor area against the 40 percent fill limit in NEC Chapter 9, so three or more wires stay legal.
You get the trade size for EMT, PVC, or RMC at once, which keeps the pull within code and easy to wire.
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 the Conduit Fit Calc Uses the Fill Tables
Each conductor has a cross-sectional area listed in NEC Chapter 9, so the tool adds them and compares the sum to the raceway.
Since three or more conductors cap fill at 40 percent, the calculator leaves room for heat and an easier pull.
It reads the area for THHN, XHHW, or other insulations, so the fit reflects the actual wire you are running.
What the Conduit Size for Wire Calculator Returns
Enter the conductors and the tool gives you:
- The smallest EMT, PVC, or RMC trade size
- Total conductor area against the 40 percent limit
- Fill percent for the chosen trade size
- Counts for mixed sizes in one run
- Insulation type per conductor
- A note if the run exceeds the fill 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
Why is the fill limit 40 percent?
NEC Chapter 9 caps fill at 40 percent for three or more conductors so the wires dissipate heat and pull without damage. The calculator applies that limit automatically.
Does conduit type change the trade size?
Yes, since EMT, PVC, and RMC have different inside diameters, the same conductors may need a different trade size in each. Pick the raceway type before reading the result.
Can I mix conductor sizes in one conduit?
Yes, enter each conductor and the conduit fit calc sums the areas. Confirm the final fill against the current NEC Chapter 9 tables 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.