Screw Length & Gauge Guide Calculator
Match wood screw gauge to pilot hole size and recommended length in inches for clean joinery.
What Is a Wood Screw Gauge?
Wood screw gaugeis the American standard numbering system that encodes shank diameter — the higher the number (#4 through #14), the wider the screw. Gauge determines pilot hole size, holding strength, and whether coarse or fine thread is appropriate for the wood species.
The Screw Length & Gauge Calculator determines the correct screw gauge, pilot hole diameter, and minimum screw length for your project. Enter the material thickness and wood type and it returns the exact drill bit sizes for softwood and hardwood pilot holes, the clearance hole, and the recommended screw lengths.
Screw Gauge Formula
The shank outer diameter of a standard wood screw can be calculated from its gauge number:
For pilot hole sizing:
For screw length selection:
This ensures at least 50–100% of the screw length engages the receiving member, providing adequate pullout resistance.
Wood Screw Gauge Reference Chart
| Gauge | Shank Dia. (in) | Pilot (Softwood) | Pilot (Hardwood) | Clearance Hole | Common Lengths |
|---|---|---|---|---|---|
| #4 | 0.112 in | 3/64 in | 1/16 in | 7/64 in | 1/2, 3/4, 1 in |
| #6 | 0.138 in | 5/64 in | 5/64 in | 9/64 in | 3/4, 1, 1-1/4 in |
| #8 | 0.164 in | 3/32 in | 7/64 in | 11/64 in | 1, 1-1/4, 1-1/2, 2 in |
| #10 | 0.190 in | 7/64 in | 1/8 in | 3/16 in | 1-1/4, 1-1/2, 2, 2-1/2 in |
| #12 | 0.216 in | 1/8 in | 9/64 in | 7/32 in | 1-1/2, 2, 2-1/2, 3 in |
| #14 | 0.242 in | 9/64 in | 5/32 in | 1/4 in | 2, 2-1/2, 3 in |
How to Select the Right Screw Length
The correct screw length ensures the tip penetrates deeply enough into the receiving member to create a strong mechanical connection, without protruding through the other side.
- Measure the combined thickness of all materials being joined.
- Determine the minimum penetration depth needed in the receiving member (at least 1× the top board thickness).
- Choose the next available commercial length that meets or exceeds this minimum.
- Verify the screw will not protrude through the receiving member.