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Calculate precise bolt clearance hole sizes instantly with our free online Clearance Hole Calculator. Supports metric & imperial sizes. Fast, easy, and accurate.
When you're working with mechanical components, fabrication, or any type of bolted assembly, choosing the correct clearance hole size is essential. A clearance hole is slightly larger than the bolt or screw itself, allowing the fastener to pass through without threading into the material.
We developed the Clearance Hole Calculator to make it incredibly easy for anyone engineers, machinists, DIYers, and students to calculate the perfect hole size for bolts, whether you’re using metric or imperial measurements.
A clearance hole is a drilled or punched hole that allows a bolt or screw to pass freely through a material. Unlike tapped holes, clearance holes do not hold the threads; instead, the fastener threads into another component or a nut on the opposite side. The purpose is to provide just enough extra space for the bolt shaft without making the hole so large that it causes instability or weakens the joint.
To determine the proper clearance hole size, you typically follow these guidelines:
Formula for clearance hole size:
Clearance Hole Diameter = Bolt Diameter + Allowance
For example:
If you are using an M8 bolt, a normal clearance hole would be:
8 mm (bolt diameter) + 0.4 mm = 8.4 mm
So, the recommended clearance hole size is 8.4 mm.
| Bolt Size | Tight Fit | Normal Fit | Loose Fit |
|---|---|---|---|
| M3 | 3.1 mm | 3.4 mm | 3.6 mm |
| M4 | 4.1 mm | 4.4 mm | 4.6 mm |
| M5 | 5.1 mm | 5.5 mm | 5.8 mm |
| M6 | 6.2 mm | 6.6 mm | 7.0 mm |
| M8 | 8.2 mm | 8.4 mm | 9.0 mm |
| M10 | 10.3 mm | 10.7 mm | 11.0 mm |
We also provide a downloadable Bolt Clearance Hole Size Chart PDF (Metric) for offline use.
For imperial bolts like the 1/4-20 (¼ inch diameter with 20 threads per inch), the standard clearance hole sizes are:
These sizes allow the bolt to pass through with the intended tolerance based on the fit you need.
The calculator removes the guesswork and speeds up your design or fabrication process.
Clearance holes might seem like a small detail, but they play a big role in the stability and alignment of mechanical joints. Using the wrong hole size can lead to misalignment, weak fastening, or even damage. Our Clearance Hole Calculator gives you an instant solution no more manual chart referencing or math errors.
Whether you're creating a metal bracket, assembling wood components, or designing a CAD model, knowing the correct clearance hole size saves time and ensures quality. Try our calculator today it’s fast, free, and supports both metric and imperial standards.
The rule of thumb is to add 0.2 mm to 0.5 mm for a normal fit and up to 1.0 mm for a loose fit in metric units. For inches, add 0.005 to 0.015 inches.
Yes. While the material may affect how the bolt sits, the calculator gives a general size for the clearance hole, regardless of material type.
Yes. We provide a downloadable PDF chart of common metric clearance hole sizes for quick reference.
Absolutely. As long as you input the correct diameter, the calculator adjusts the clearance accordingly.
Yes, this tool is built to help professionals and hobbyists alike with fast, accurate clearance hole calculations.