WireGaugeCalc Free calculator · NEC cited · works offline
Maximum Wires In Rigid Metal Conduit
Maximum wires in rigid metal conduit is fast with WireGaugeCalc, which counts conductors against the NEC 40 percent fill limit.
It reads the RMC areas from NEC Chapter 9, so you do not look up the numbers.
Choose the RMC size and wire and the count is ready.
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.
Filling Rigid Metal Conduit To Code
The tool divides 40 percent of the RMC area by the conductor area, since three or more wires hold fill at 40 percent.
It uses the rigid metal conduit dimensions from NEC Chapter 9, so the result matches the table.
It handles mixed gauges by adding up the total conductor area.
Inputs For An RMC Wire Count
Enter these to get the conductor limit for rigid metal conduit:
- RMC trade size, such as 1 or 1-1/4 inch
- Wire gauge, like 8 or 6 AWG
- Insulation type, such as THWN
- Number of current-carrying conductors
- Whether a ground is included
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
How many 6 AWG THWN wires fit in 1 inch RMC?
Under the 40 percent fill limit, 1 inch RMC holds seven 6 AWG THWN conductors. Confirm the number with the current NEC Chapter 9 tables and your local authority having jurisdiction.
Is RMC fill different from EMT fill?
The 40 percent fill rule is the same, but the internal area differs by conduit type. Rigid metal conduit and EMT have different dimensions, so use the RMC column for an accurate count.
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.