Conduit Fill
Check whether THHN conductors fit inside EMT, PVC Schedule 40, or RMC conduit using NEC Chapter 9 fill allowances (53%, 31%, 40%). Supports up to two conductor groups and nipple/sleeve mode (60%).
Formula: Fill % = total conductor area / conduit internal area — NEC Ch. 9 Tables 1, 4, 5
Conductor Group 1 (THHN)
Conductor Group 2 (optional)
How this calculator works
Check whether THHN conductors fit inside EMT, PVC Schedule 40, or RMC conduit using NEC Chapter 9 fill allowances (53%, 31%, 40%). Supports up to two conductor groups and nipple/sleeve mode (60%).
Formula
Fill % = total conductor area / conduit internal area — NEC Ch. 9 Tables 1, 4, 5How to use it
- Collect current field measurements and known project values.
- Enter each value and confirm that every selected unit matches your measurements.
- Review the calculated result, then verify it against plans, product data, site conditions, and applicable codes.
Worked example
For a representative electrical job, enter the measured values from one area first and calculate the result. Repeat the calculation for each area whose dimensions or conditions differ, add the results, and apply only the waste or contingency allowance the project actually requires. This keeps unlike conditions from being hidden inside one average.
Frequently asked questions
What formula does the Conduit Fill calculator use?
The calculator uses: Fill % = total conductor area / conduit internal area — NEC Ch. 9 Tables 1, 4, 5. Results are planning estimates and should be checked against project requirements, manufacturer data, and applicable codes.
How accurate is the Conduit Fill calculator?
Accuracy depends on the measurements and assumptions you enter. Use current field measurements, include an appropriate waste or safety allowance when the form provides one, and verify the result before purchasing or installing materials.
Can I use this electrical result for a final quote?
Use it as a starting point for planning. A final quote should also account for site conditions, labor, taxes, permits, local code requirements, and supplier packaging or minimum-order rules.