Clearance Hole Calculator

Find the right drill bit size for a clearance or pilot hole.

How the Math Works

The Clearance Hole Calculator uses the fundamental formula: hole = bolt diameter × fit factor. This equation determines the appropriate hole size needed for a screw to pass through with the correct amount of clearance. The fit factor is a multiplier that accounts for manufacturing tolerances and the type of fit required - for example, a close fit might use a factor of 1.05, while a loose fit could use 1.25. Simply multiply your screw's nominal diameter by the appropriate fit factor to get the exact drill bit size needed.

Practical Applications

To use this calculator practically, first measure or identify your screw's bolt diameter, then select the appropriate fit factor based on your application needs. For precision work, choose a fit factor between 1.02 and 1.08 for minimal clearance. For general construction, use 1.10 to 1.20 for easier assembly. For disassembled maintenance or soft materials, select 1.25 or higher. This ensures you purchase the correct drill bits and avoid common mistakes like drilling holes that are too small or too large for your hardware.

Day-to-Day Use

This calculator prevents frustrating delays in everyday projects like furniture assembly, where you might be stuck with incompatible screws and holes. It's useful for DIY home repairs, crafting projects, or when installing curtain rods and shelves. By calculating the right clearance before drilling, you avoid having to redrill larger holes or scrape out stripped screw holes, saving both time and materials in your daily workshop tasks and household improvements.

Worked example

1/4 in screw, normal clearance → 0.275 in.

FAQ