What size hole saw for 1/2" conduit?
Into a box or panel, the hole for 1/2" conduit is sized for the connector, not the pipe: it's the standard 7/8" knockout.
That's true for EMT, PVC and rigid conduit alike. Passing the conduit itself through a stud or wall is a different size, shown below.
Nominal size
Change the size to compare. Under each, the pipe’s real outside diameter.
Hole saw for 1/2-inch conduit, by job
The knockout size (NEMA 0.875"), for the connector rather than the pipe.
The conduit is 0.840" across. Exact fit: 7/8".
EMT is smaller: 0.706" across. Exact fit: 3/4".
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Why the box hole isn’t the pipe’s size
The 7/8" hole matches the knockouts stamped into boxes and panels, so a connector and locknut seat exactly as they would in a factory knockout. In a thin steel box, a step drill bit that reaches 7/8" also cuts this hole.
Same trap as wood: lumber sizes, nominal vs actual.
Box, panel or stud
Into a box, the hole is sized for the connector’s threaded end and locknut, which is why it’s the knockout size rather than the conduit’s. In a thin steel box, a step drill bit or a knockout punch cuts the same hole; see what drill bit for metal for cutting steel. Through studs and joists, the hole only has to clear the pipe, and the code limits it by the lumber’s depth: how big a hole you can drill in a stud.
Common questions
What size hole saw for 1/2 inch conduit?
Into a box or panel, use a 7/8" hole saw, the standard 1/2" knockout (NEMA 0.875"). It's the same for EMT, PVC and rigid conduit, because the hole fits the connector, not the pipe.
What size hole for 1/2 inch conduit through a stud?
Through framing, the hole follows the pipe: 1" for 1/2" PVC or rigid conduit (0.840" across), or 7/8" for 1/2" EMT (0.706" across).
Is a 1/2" knockout the same as a 1/2" hole?
No. A "1/2 inch" knockout is named for the conduit trade size; the hole itself is 0.875" (NEMA), cut with a 7/8" hole saw or a knockout punch.
Full hole saw chart
Hole saw size chart for pipe and conduit
| PVC / ABS | Actual OD | Easy clearance | Exact fit | Clear a coupling |
|---|---|---|---|---|
| 1/2" | 0.840"21.3 mm | 1"25.4 mm | 7/8"22.2 mm | 1-5/16"hub 1-3/32" |
| 3/4" | 1.050"26.7 mm | 1-3/16"30.2 mm | 1-1/16"27 mm | 1-7/16"hub 1-5/16" |
| 1" | 1.315"33.4 mm | 1-1/2"38.1 mm | 1-3/8"34.9 mm | 1-3/4"hub 1-5/8" |
| 1-1/4" | 1.660"42.2 mm | 1-13/16"46 mm | 1-11/16"42.9 mm | 2-1/8"hub 1-31/32" |
| 1-1/2" | 1.900"48.3 mm | 2-1/16"52.4 mm | 1-15/16"49.2 mm | 2-3/8"hub 2-7/32" |
| 2" | 2.375"60.3 mm | 2-1/2"63.5 mm | 2-3/8"zero clearance | 2-7/8"hub 2-3/4" |
| 2-1/2" | 2.875"73 mm | 3"76.2 mm | 2-7/8"zero clearance | 3-1/2"hub 3-11/32" |
| 3" | 3.500"88.9 mm | 3-5/8"92.1 mm | 3-1/2"zero clearance | 4-1/8"hub 4" |
| 4" | 4.500"114.3 mm | 4-5/8"117.5 mm | 4-1/2"zero clearance | 5-1/2"hub 5-1/32" |
| Copper / PEX | Actual OD | Easy clearance | Exact fit |
|---|---|---|---|
| 3/8" | 0.500"12.7 mm | 5/8"15.9 mm | 9/16"14.3 mm |
| 1/2" | 0.625"15.9 mm | 3/4"19 mm | 5/8"zero clearance |
| 3/4" | 0.875"22.2 mm | 1"25.4 mm | 7/8"zero clearance |
| 1" | 1.125"28.6 mm | 1-5/16"33.3 mm | 1-1/8"zero clearance |
| 1-1/4" | 1.375"34.9 mm | 1-1/2"38.1 mm | 1-3/8"zero clearance |
| 1-1/2" | 1.625"41.3 mm | 1-3/4"44.4 mm | 1-5/8"zero clearance |
| 2" | 2.125"54 mm | 2-1/4"57.2 mm | 2-1/8"zero clearance |
| Conduit | Into a box | Through, PVC / rigid | Through, EMT |
|---|---|---|---|
| 1/2" | 7/8"NEMA 0.875" | 1"exact 7/8" | 7/8"exact 3/4" |
| 3/4" | 1-1/8"NEMA 1.109" | 1-3/16"exact 1-1/16" | 1-1/16"exact 15/16" |
| 1" | 1-3/8"NEMA 1.375" | 1-1/2"exact 1-3/8" | 1-5/16"exact 1-3/16" |
| 1-1/4" | 1-3/4"NEMA 1.734" | 1-13/16"exact 1-11/16" | 1-11/16"exact 1-9/16" |
| 1-1/2" | 2"NEMA 1.984" | 2-1/16"exact 1-15/16" | 1-7/8"exact 1-3/4" |
| 2" | 2-1/2"NEMA 2.469" | 2-1/2"exact 2-3/8" | 2-3/8"exact 2-1/4" |
| 2-1/2" | 3"NEMA 2.969" | 3"exact 2-7/8" | n/a |
| 3" | 3-5/8"NEMA 3.594" | 3-5/8"exact 3-1/2" | n/a |
| 4" | 4-5/8"NEMA 4.641" | 4-5/8"exact 4-1/2" | n/a |
Easy clearance = smallest saw at least 1/8" over the pipe’s outside diameter (about 1/16" around it), the default. Exact fit = smallest saw at least the pipe’s outside diameter; “zero clearance” means the saw equals the pipe’s nominal outside diameter: it can bind, and pipe at the top of its tolerance won’t pass. Clear a coupling = the Sch 40 coupling hub plus 1/8". Into a box, conduit follows the NEMA knockout for the trade size, the same for EMT, PVC and rigid.
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Where these numbers come from
Outside diameters are copied from the makers’ and standards’ published tables. The hole saw sizes are not typed in: they’re worked out from those diameters and the sizes saw makers actually sell, then checked at build time so a recommended hole can never be smaller than what has to pass through it. Easy clearance is the smallest saw at least 1/8" bigger than the pipe; exact fit is the smallest saw at least the pipe’s size. Millimetres are converted from inches, not copied.
- Atkore / Allied, EMT submittal (UL 797 / ANSI C80.3)
- Atkore / Allied, rigid conduit (GRC) sheet (UL 6 / ANSI C80.1)
- Atkore Heritage Plastics, PVC conduit catalog (UL 651 / NEMA TC 2)
- 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)
- Starrett, Saws & Hand Tools catalogue (bi-metal sizes)
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.