Conduit Fill Calculator
Check whether conductors fit in a conduit per NEC fill limits.
Inputs
Results
Result
PASS
| Result | PASS |
|---|---|
| Fill % | 7.5 % |
| Allowed Fill | 40 % |
| Total Wire Area | 0.0399 in² |
| Conduit Area | 0.5330 in² |
| Min. Suggested Size | - " |
· Max fill for 3 conductor(s) is 40% (NEC Ch 9, Table 1).
· Wire areas in this tool are for THHN/THWN-2. Other insulation has different diameters.
How It Works
NEC Chapter 9, Table 1 max fill: 1 conductor: 53% 2 conductors: 31% 3 or more: 40% Wire areas in this tool are for THHN/THWN-2 (NEC Ch 9, Table 5). Other insulations have different diameters.
Example
Three 12 AWG THHN in 3/4" EMT: 3 x 0.0133 in² = 0.0399 in². Conduit area 0.533 in². Fill = 7.5%, under the 40% limit.
Frequently Asked Questions
Why is the limit different for 1 or 2 conductors?
Heat and pull tension change with conductor count. NEC Table 1 spells out the percentages.
Does this include equipment grounding conductors?
Yes. Every conductor in the conduit counts, including grounds.
Are these areas for THHN only?
This calculator uses THHN/THWN-2 areas. Other insulation types (XHHW, RHH, etc.) have different diameters. Always verify against NEC Chapter 9, Table 5.
These numbers are for reference only. We are not liable for any decisions you make or how you use these results in the real world. Check the current NEC and your local codes, and have a licensed electrician sign off before you install or buy. Full disclaimer