Conduit knockout sizes (free printable PDF)
A conduit hole in a box or panel is sized for the connector, not the pipe. 1/2" conduit takes a 7/8" knockout, whether it's EMT, PVC or rigid.
Conduit knockout sizes
| Trade size | Knockout | NEMA range | Hole saw | Punch cuts |
|---|---|---|---|---|
| 1/2" | 0.875"22.2 mm | 0.859–0.906" | 7/8" | 0.885" |
| 3/4" | 1.109"28.2 mm | 1.094–1.141" | 1-1/8" | 1.115" |
| 1" | 1.375"34.9 mm | 1.359–1.406" | 1-3/8" | 1.362" |
| 1-1/4" | 1.734"44.0 mm | 1.719–1.766" | 1-3/4" | 1.701" |
| 1-1/2" | 1.984"50.4 mm | 1.958–2.016" | 2" | 1.951" |
| 2" | 2.469"62.7 mm | 2.433–2.500" | 2-1/2" | 2.416" |
| 2-1/2" | 2.969"75.4 mm | 2.938–3.000" | 3" | 2.914" |
| 3" | 3.594"91.3 mm | 3.563–3.625" | 3-5/8" | 3.539" |
| 4" | 4.641"117.9 mm | 4.563–4.672" | 4-5/8" | 4.544" |
Knockout and range: NEMA’s industry guideline (not code). Hole saw: the size the saw maker lists for the trade size, always inside NEMA’s range. Punch cuts: what Greenlee and Milwaukee knockout punches cut, a few thousandths small; both fit standard connectors. The same for EMT, PVC and rigid conduit.
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How to read it
Find the conduit trade size and read across. The hole is sized for the connector and locknut, so it’s bigger than the conduit’s nominal size and the same for every conduit type. Through a stud, the hole follows the pipe instead: see the hole saw size finder.
Common questions
What size is a 1/2 inch knockout?
0.875" (NEMA), cut with a 7/8" hole saw. The "1/2 inch" is the conduit trade size, not the hole.
Is the knockout the same for EMT, PVC and rigid conduit?
Yes. The knockout is sized for the connector of that trade size, so it's the same whichever conduit the connector is for.
Why does my knockout punch cut slightly smaller?
Punch makers size their punches a few thousandths under NEMA's nominal. Both the punched and the sawn hole fit standard connectors and locknuts.
Gear for this job
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Where these numbers come from
Knockout diameters and ranges from NEMA Engineering Bulletin 71, an industry guideline rather than code. Hole saw sizes are the ones the saw maker lists for each trade size, each checked at build time to sit inside NEMA’s range. Punch sizes from the punch makers’ catalogs.
- NEMA Engineering Bulletin No. 71, Knockout Diameters and Fitting Dimensions
- Greenlee, Slug-Buster knockout punch catalog
- Milwaukee, Knockout System hole guide
- Lenox, Hole Saws & Accessories catalog (sizes sold; pipe-entrance table)
General sizing guidance from published pipe, conduit and hole saw dimensions. Before boring framing, check the hole limits in your local building code; for electrical work, follow your local electrical code and the fitting maker's instructions.