Clearance Hole Calculator
Calculate clearance hole accurately for your build. Get material quantities, waste allowances, and project cost breakdowns.
Reviewed by Abdullah, Technical Content Specialist
Formula
Hole Diameter = Bolt Diameter x Fit Factor
The clearance hole diameter is calculated by multiplying the nominal bolt diameter by a fit factor. Close fit uses a factor of approximately 1.06, normal fit uses 1.12, and loose fit uses 1.25. The radial clearance is half the difference between the hole and bolt diameters.
Worked Examples
Example 1: M10 Normal Fit Clearance Hole
Problem:Find the clearance hole diameter for an M10 bolt using normal fit class.
Solution:Hole Diameter = Bolt Diameter x Fit Factor\nHole Diameter = 10 x 1.12 = 11.200 mm\nClearance per side = (11.2 - 10) / 2 = 0.600 mm
Result:11.200 mm hole diameter with 0.600 mm radial clearance
Example 2: M6 Close Fit for Precision Assembly
Problem:Determine the clearance hole for an M6 bolt in a close fit application.
Solution:Hole Diameter = 6 x 1.06 = 6.360 mm\nClearance per side = (6.36 - 6) / 2 = 0.180 mm
Result:6.360 mm hole diameter with 0.180 mm radial clearance
Frequently Asked Questions
What is a clearance hole and why is it needed?
A clearance hole is a through-hole drilled larger than the bolt or screw that passes through it. The extra space allows the fastener to slide through freely without engaging the threads, ensuring the clamping force is applied by the bolt head and nut rather than thread friction. Clearance holes also compensate for minor misalignment between mating parts during assembly.
What are the different fit classes for clearance holes?
There are three standard fit classes defined by ISO 273 and ASME B18.2.8. Close fit provides minimal clearance (about 6% oversize) for precision assemblies. Normal fit adds moderate clearance (about 12% oversize) and is the most commonly used class. Loose fit offers generous clearance (about 25% oversize) for structural steel and applications where alignment tolerance is needed.
Does the clearance hole size affect joint strength?
The clearance hole itself does not significantly affect the clamping strength of a bolted joint, as long as the washer or bolt head fully covers the hole. However, excessively large clearance holes can reduce the bearing area under the bolt head, which may require larger washers. In shear-loaded joints, smaller clearance holes provide better load transfer and reduce slip before the bolt bears on the hole wall.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy