Screw & Pilot Hole Calculator
A screw without a pilot hole is a split board waiting to happen. Enter your screw and board thickness to get the right length and drill size.
Workshop AI assistant
Describe the piece you want to build and get a complete plan: dimensions, cut list, materials, cost, steps, tools and time.
Workshop assistant
Describe the piece you want to build and get a complete plan: dimensions, cut list, materials, cost, steps, tools and time.
AI-generated results are indicative. Verify dimensions, loads and local codes before building.
How it works
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1
Enter the screw gauge (4–16) — the tool converts it to a diameter in mm.
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2
Set the screw length and the thickness of the top board.
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3
Choose softwood or hardwood.
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4
Calculate: shank pilot, thread pilot, recommended screw length and penetration.
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5
Drill the pilot hole, then drive the screw.
Formula
Diameter: gauge → mm (approx. 0.16 × gauge + 0.6, standard gauges: 6 = 3.5, 8 = 4.2, 10 = 4.8, 12 = 5.5 mm). Thread pilot ≈ 60% of diameter (softwood) or 85% (hardwood). Shank pilot ≈ 95% of diameter. Screw length ≈ 2 × thickness of the top board. Penetration = screw length − top board thickness.
Practical tips
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Drill the pilot a hair smaller than recommended if the joint will be load-bearing.
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Countersink or use a countersunk bit so screw heads sit flush.
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In hardwood near the edge, drill a pilot and drive slowly.
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For cabinet hinges, match the screw to the hinge holes and use the thread pilot.
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Wax the screw or use soap to ease driving in hard woods.
Common mistakes
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Skipping the pilot hole in hardwood near the edge.
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Using a screw so short it never reaches the substrate.
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Driving a self-tapping screw into MDF without a pilot and blowing the face.
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Choosing a screw longer than the total thickness and poking through.
Disclaimer
These results are indicative only. Always verify against local building codes, standards and professional advice before building.
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CalculateRelated guides
- How to Build a Wooden Table A complete beginner-to-intermediate walkthrough: design, cut, assemble and finish a dining table.
- How to Choose Wood Thickness Match panel and board thickness to the job: shelves, carcasses, tops and structural parts.
- Woodworking Joinery Guide From butt joints to dovetails: the strength, tools and uses of common joints.
- Choosing Screws and Drilling Pilot Holes Screw gauges, the length rule and pilot-hole sizes that stop wood from splitting.
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