Find Your Drill-Bit Size
Choose the closest screw and the material you are working with.
Pilot Hole Size Calculator
Choose a common wood screw, material and hole type to get a practical drill-bit starting size in metric and imperial units.
Designed for practical wood-screw setupSelect the screw, material and hole type to get a reference starting size. Results are intended for common wood screws; fastener-specific manufacturer guidance takes priority.
I don't know my screw size
Measure the screw's outside/major diameter with a ruler or caliper. If possible, also measure the threaded root diameter. The measurement result is a starting point, not a manufacturer specification.
Understand the three hole types
Pilot hole: a smaller hole in the receiving piece that helps the screw enter with less splitting and driving resistance.
Clearance hole: a hole through the upper piece that lets the screw shank pass through so the joint can clamp.
Countersink: a recess for a compatible flat/countersunk screw head. The correct diameter depends on the actual screw head, not just the screw's nominal diameter.
Important: there is no single universal pilot-hole size. Screw design, wood density, grain direction and the manufacturer's installation guidance can change the recommendation. Structural/self-drilling screws may be designed for different installation methods.
Reference method
For the common #6–#14 wood-screw options, the calculator now uses a fixed reference table rather than the previous arbitrary material-factor formula. Plywood follows the softwood reference and MDF/particleboard follows the hardwood reference as a practical starting convention. Metric options use a separate metric wood-screw reference table; they are deliberately labelled by diameter rather than “M” because an M-size can also refer to a machine-thread fastener, which is a different application.
Published references do not agree perfectly on every screw design, so these values are presented as starting references rather than guaranteed specifications.
Common wood-screw reference
| Screw | Softwood | Hardwood | Clearance | Countersink* |
|---|---|---|---|---|
| #6 | 5/64" · 2.0 mm | 3/32" · 2.4 mm | 9/64" · 3.6 mm | 9/32" · 7.1 mm |
| #8 | 7/64" · 2.8 mm | 1/8" · 3.2 mm | 11/64" · 4.4 mm | 5/16" · 8.0 mm |
| #10 | 1/8" · 3.2 mm | 9/64" · 3.6 mm | 3/16" · 4.8 mm | 3/8" · 9.5 mm |
| #12 | 9/64" · 3.6 mm | 5/32" · 4.0 mm | 7/32" · 5.6 mm | 7/16" · 11.0 mm |
| #14 | 5/32" · 4.0 mm | 11/64" · 4.4 mm | 1/4" · 6.4 mm | 1/2" · 12.7 mm |
*Countersink values are reference values for compatible flat/countersunk heads; actual screw-head geometry should take priority.
How to use the calculator
- Select the screw closest to your fastener.
- Select the material.
- Choose pilot, clearance or pilot + countersink.
- Use the displayed metric and imperial value to select a practical bit.
- For an important joint, test on scrap of the same material and verify the fastener manufacturer's instructions.
Frequently asked questions
What size pilot hole does a #8 wood screw need?
The reference table uses 2.8 mm (7/64") in softwood and 3.2 mm (1/8") in hardwood. Different screw designs and wood species can require adjustment.
Why is the hardwood pilot larger?
Denser wood generally gives the screw less room to displace fibers, so a larger pilot can reduce splitting and driving resistance.
Is a clearance hole the same as a pilot hole?
No. A clearance hole is intended to let the screw shank pass through the upper piece, while the pilot hole is for the receiving piece where the threads engage.
Should I always use the exact calculated size?
No. Treat the result as a reference starting point. Fastener geometry, wood species, grain direction, proximity to an edge and manufacturer guidance can change the appropriate size.
What about modern self-drilling or structural screws?
Some engineered fasteners are specifically designed to reduce or eliminate pre-drilling in certain wood applications. Follow the instructions for the exact fastener instead of assuming this chart applies.
Sources & methodology
The reference table is based on published wood-screw pilot/clearance charts and is intentionally presented as a practical starting reference rather than a universal standard. Manufacturer-specific instructions take priority.