Select a wood-screw gauge and wood category. Values follow McFeely’s straight-pilot recommendations and separate shank-hole sizes. A tapered drill is a different tool and uses a different row of that chart.
Product-specific screw instructions take precedence.
This lookup covers the selected gauges only and is not a structural-fastener schedule. Screw design, wood condition, depth and proximity to an edge affect the installation. Check the screw maker’s instructions and try a scrap sample.
Pilot hole diameter (inches) from screw gauge
| Screw gauge | #8 wood screw |
|---|---|
| Wood type | Softwood (pine, fir, spruce) |
| Pilot hole diameter (inches) | 0.109 |
| Clearance hole diameter (inches) | 0.172 |
Common error: Skipping the pilot near an edge or end of the board. That is where wood splits most easily, and a small hole prevents it.
Fastener Pilot & Clearance Hole Reference: formula
NIST Handbook 44: Units and Systems of Measurement · McFeely’s: Drilling chart
Fastener Pilot & Clearance Hole Reference: changing Screw gauge
| Screw gauge | Pilot hole diameter (inches) | Clearance hole diameter (inches) |
|---|---|---|
| 4 | 0.063 | 0.109 |
| 6 | 0.094 | 0.141 |
| 8 (example) | 0.109 | 0.172 |
| 10 | 0.125 | 0.203 |
| 12 | 0.141 | 0.219 |
Fastener Pilot & Clearance Hole Reference: compare input ranges
| Input | Tested from | To | Pilot hole diameter (inches): low input | Pilot hole diameter (inches): high input | Swing |
|---|---|---|---|---|---|
| Screw gauge | #4 wood screw | #12 wood screw | 0.063 | 0.141 | 0.078 (71%) |
| Wood type | Softwood (pine, fir, spruce) | Hardwood (oak, maple, cherry) | 0.109 | 0.125 | 0.016 (14%) |
Fastener Pilot & Clearance Hole Reference: individual input comparisons
| Input | Value | Pilot hole diameter (inches) | Clearance hole diameter (inches) |
|---|---|---|---|
| Screw gauge | #4 wood screw | 0.063 | 0.109 |
| #6 wood screw | 0.094 | 0.141 | |
| #8 wood screw | 0.109 | 0.172 | |
| #10 wood screw | 0.125 | 0.203 | |
| #12 wood screw | 0.141 | 0.219 | |
| Wood type | Softwood (pine, fir, spruce) | 0.109 | 0.172 |
| Hardwood (oak, maple, cherry) | 0.125 | 0.172 |
Fastener Pilot & Clearance Hole Reference: values and definitions
| Quantity and definition | Value used |
|---|---|
| Screw gauge — Wood screw gauge. | #8 wood screw |
| Wood type — Softwood or hardwood; hardwood needs a slightly larger pilot hole. | Softwood (pine, fir, spruce) |
| Pilot hole diameter (inches) | 0.109 |
| Clearance hole diameter (inches) | 0.172 |
A pilot hole gives a screw's threads material to bite into without splitting the wood, and the clearance hole lets the screw pass through the top piece freely. For a number 8 wood screw in softwood, the pilot is about 1/8 inch and the clearance hole about 5/32. Hardwood needs a slightly larger pilot, since it cannot compress around the threads.
A hole that is too small splits the wood, and one that is too large leaves the screw loose.
Test in a scrap of the same wood, and drill a little deeper than the screw's threaded length. The pilot only needs to reach the threaded part.
See the cut list calculator for sheet goods, the fence and drywall pages for larger builds, and the torque converter for fastener torque. The unit conversion pages convert fractions of an inch to millimeters, and the length converter helps with drill sizes.
Why do I need a pilot hole?
It guides the screw and prevents the wood from splitting, especially near edges and in hardwoods.
What is a clearance hole?
A larger hole in the top piece, sized for the screw's shank, so the screw pulls the pieces together instead of holding them apart.
Are pilot holes needed for self-drilling screws?
Often not in softwood or metal, but hardwoods and edges still benefit from a pilot to prevent splitting.