How electricians check conduit fill
If the wires already exist, the question is whether they fit the pipe — not what AWG the load wants.
Open the conduit fill calculator
How to run this check
- Count every conductor you are pulling, including the equipment ground if it is in the raceway.
- Pick EMT or PVC and the trade size on the wall.
- Read fill percent, the planning limit, and the next trade size if it fails.
The three planning limits
One conductor: 53%. Two conductors: 31%. Three or more: 40%. Those are the planning limits this site uses.
Nipples and some local rules differ. This page does not approve a pull and it does not reprint a copyrighted table.
Fill and ampacity are different jobs
A pipe can be under 40% fill and still need ampacity adjustment because of conductor count and heat.
After a wire-size upsize, come back here. The larger AWG you just bought may no longer fit the 1/2 in you planned.
THHN in EMT, planning areas only
| Pull | Trade size | Fill | Limit | Verdict |
|---|---|---|---|---|
| 3x 12 AWG + 1x 12 AWG ground | 1/2 in EMT | 17.5% | 40% | Fits |
| 9x 12 AWG THHN | 1/2 in EMT | 39.4% | 40% | Fits |
Related
FAQ
Does the ground count?
If it is in the raceway, count it for fill. This site does not guess hidden grounds.
Is a fail the same as illegal?
It means this planning check is over the limit we use. Verify the current tables and the AHJ before you pull.
Planning reference only. Verify against the current NEC, manufacturer data, and the authority having jurisdiction. This is not engineering advice or a license substitute.