Clearance Hole Calculator

Calculator Inputs

Calculation mode

Fastener system

Reference standard

Fastener type

Fastener size

Fit type

Existing hole diameter

Custom fastener diameter

Custom clearance allowance

Clearance basis

Input units

Result units

Decimal precision

Negative tolerance

Positive tolerance

Preferred drill series

Material

Hole-making process

Calculate countersink

Calculate counterbore

Fastener head diameter

Fastener head height

Countersink included angle

Head diameter allowance

Counterbore depth allowance

Clearance-hole values vary by standard, manufacturer, coating, and process. Confirm critical dimensions against approved drawings.

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Formula Used

Clearance hole diameter = fastener diameter + diametral clearance

Diametral clearance = clearance hole diameter − fastener diameter

Radial clearance = diametral clearance ÷ 2

Standard mode uses listed reference diameters. Custom mode applies your selected clearance. Always verify the governing drawing before production.

How to Use This Calculator

Select the calculation mode and fastener system.
Choose a standard, fastener size, and fit.
Set tolerances, units, and preferred drill series.
Add optional countersink or counterbore dimensions.
Calculate, then review warnings and drill guidance.

Example Data

Fastener	Fit	Hole	Typical use
M6	Close	6.4 mm	Accurate positioning
M8	Normal	9.0 mm	General assembly
M12	Loose	14.5 mm	Greater alignment freedom
1/4 in	Normal	0.266 in	General inch-series assembly
1/2 in	Loose	0.5625 in	Field assembly tolerance

Hole Type Differences

Hole type	Purpose	Main dimension
Clearance hole	Lets a fastener pass freely	Larger than fastener diameter
Tapping hole	Provides material for internal threads	Smaller than major thread diameter
Counterbore	Recesses a cylindrical fastener head	Diameter and flat-bottom depth
Countersink	Recesses a conical fastener head	Outer diameter, angle, and depth

Common Metric Clearance Reference

Size	Nominal	Close	Normal	Loose
M2	2.0 mm	2.2 mm	2.4 mm	2.6 mm
M2.5	2.5 mm	2.7 mm	2.9 mm	3.1 mm
M3	3.0 mm	3.2 mm	3.4 mm	3.6 mm
M4	4.0 mm	4.3 mm	4.5 mm	4.8 mm
M5	5.0 mm	5.3 mm	5.5 mm	5.8 mm
M6	6.0 mm	6.4 mm	6.6 mm	7.0 mm
M8	8.0 mm	8.4 mm	9.0 mm	10.0 mm
M10	10.0 mm	10.5 mm	11.0 mm	12.0 mm
M12	12.0 mm	13.0 mm	13.5 mm	14.5 mm
M14	14.0 mm	15.0 mm	15.5 mm	16.5 mm
M16	16.0 mm	17.0 mm	17.5 mm	18.5 mm
M18	18.0 mm	19.0 mm	20.0 mm	21.0 mm
M20	20.0 mm	21.0 mm	22.0 mm	24.0 mm
M22	22.0 mm	23.0 mm	24.0 mm	26.0 mm
M24	24.0 mm	25.0 mm	26.0 mm	28.0 mm
M27	27.0 mm	28.0 mm	30.0 mm	32.0 mm
M30	30.0 mm	31.0 mm	33.0 mm	35.0 mm
M33	33.0 mm	34.0 mm	36.0 mm	38.0 mm
M36	36.0 mm	37.0 mm	39.0 mm	42.0 mm
M39	39.0 mm	40.0 mm	42.0 mm	45.0 mm
M42	42.0 mm	43.0 mm	45.0 mm	48.0 mm
M45	45.0 mm	46.0 mm	48.0 mm	52.0 mm
M48	48.0 mm	50.0 mm	52.0 mm	56.0 mm
M52	52.0 mm	54.0 mm	56.0 mm	62.0 mm
M56	56.0 mm	58.0 mm	62.0 mm	66.0 mm
M60	60.0 mm	62.0 mm	66.0 mm	70.0 mm
M64	64.0 mm	66.0 mm	70.0 mm	74.0 mm

Frequently Asked Questions

What is a clearance hole?

A clearance hole lets a fastener pass without threading. Its diameter exceeds the fastener diameter. The final size depends on fit requirements.

What is close fit?

Close fit provides limited assembly movement. It supports accurate component positioning. Manufacturing control must remain suitably tight.

What is normal fit?

Normal fit suits general mechanical assembly. It balances alignment and easy installation. Many workshop applications use this fit.

What is loose fit?

Loose fit allows greater assembly movement. It helps with field alignment issues. Excess movement may reduce positional accuracy.

Is a clearance hole a tapping hole?

No, these holes serve different purposes. Tapping holes retain material for threads. Clearance holes let fasteners pass through.

Why select the next larger drill?

An undersized drill can block assembly. The calculator selects a suitable larger size. Production tolerances still require inspection.

Do coatings affect hole size?

Coatings can reduce effective hole diameter. Thick finishes may require added allowance. Confirm dimensions after finishing operations.

Can laser-cut holes use these values?

Yes, but kerf and taper matter. Heat effects can change final dimensions. Inspect completed parts before accepting them.

How accurate are the reference tables?

They provide practical common values. Standards and manufacturers may publish differences. Approved specifications always control final production.

Should I use countersink results directly?

Use them as preliminary geometry guidance. Head shapes and standards can differ. Verify the actual fastener before machining.

Engineering disclaimer: This calculator provides general planning guidance. It does not replace approved drawings, standards, inspection, or professional engineering review.