WireGaugeCalc Free calculator · NEC cited · works offline
Calculating Conduit Fill
calculating conduit fill is quick with WireGaugeCalc, since you pick the conduit type and add each conductor by size.
It totals the conductor cross-sectional area and compares it to the conduit area from NEC Chapter 9, so you know the fill percent.
You get a pass or fail against the 40 percent limit, so you can right-size the raceway before you pull.
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.
The 40 Percent Fill Limit Explained
For three or more conductors the NEC caps fill at 40 percent of the conduit interior, so the wires pull freely and shed heat.
The calculator reads the area for EMT, PVC, or RMC and the area of each conductor from the Chapter 9 tables.
When the total crosses 40 percent the tool flags it, so you step up to the next trade size.
Inputs for an Accurate Fill Result
Fill depends on a handful of details:
- Conduit type, EMT, PVC, or RMC
- Trade size of the raceway
- Gauge and insulation type of each conductor
- Total count of conductors in the run
- The applicable fill limit, 40 percent for three or more
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 limit 40 percent and not higher?
The 40 percent cap for three or more conductors leaves room to pull without damaging insulation and lets heat dissipate. The figure comes from NEC Chapter 9, so verify it against the current NEC and your local authority having jurisdiction.
Does insulation type change the fill?
Yes, since THHN and XHHW have different cross-sectional areas for the same gauge. Pick the exact insulation so the area total is correct.
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.