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Clearance Hole Calculator

Table of contents

What is a clearance hole?Clearance hole formulaHow to use the clearance hole calculator: an exampleClearance hole chartsFAQs

Omni Calculator's clearance hole calculator helps you to calculate the size of the hole that allows a screw to pass through a substrate without damaging the material. So whether you are planning to install some furniture or work on a DIY build, this is the perfect tool for you.

Keep reading if you want to learn how to calculate the clearance hole and check for clearance hole sizes with the clearance hole charts that we will show you.

What is a clearance hole?

A clearance hole is a hole through an object or substrate which enables threads of a screw or bolt to pass through. This hole will allow a screw to pass into a substrate without the threads biting into the material.

Since you are interested in this topic, why not check out our pitch diameter calculator or our bolt torque calculator?

Clearance hole formula

The clearance hole formula is very easy, and you can calculate it manually. You just need to add the diameter of the fastener and the diameter of the head, then divide it by 2:

CH = (DF + DH) / 2

where:

  • CH — Clearance Hole;
  • D — Diameter of the fastener; and
  • DH — Diameter of the fastener head.

The diameters are given in millimeters (metric units) or inches (imperial units). You can choose the unit in our calculator or use the length converter to convert the units.

How to use the clearance hole calculator: an example

Using this calculator is easy-peasy! Let's see an example:

  1. First, we have to insert the fastener diameter. Let's say we have a fastener that's 5 mm in diameter.

  2. Next, insert the fastener head diameter. For this same fastener, the head diameter is 8.5 mm, so we input this value in the corresponding field.

  3. Finally, the calculator will give us the result: 6.5 mm.

Clearance hole charts

The American Society of Mechanical Engineers establishes the clearance hole sizes in the ASME B18.2.8.

The standard covers the recommended clearance hole sizes for #0 through 1.5 in and M1.6 through M100 metric fasteners in three classes of clearing using a close, normal, and loose-fit category.

Below, you can find some values taken from the ASME standard.

Clearance hole chart for metric fasteners.

Nominal Screw Size

Fit Class - Normal

Fit Class - Close

Fit Class - Loose

Drill Size

Min CH

Max CH

Drill Size

Min CH

Max CH

Drill Size

Min CH

Max CH

M1.6

1.8

1.8

1.94

1.7

1.7

1.8

2

2

2.25

M2

2.4

2.4

2.54

2.2

2.2

2.3

2.6

2.6

2.85

M2.5

2.9

2.9

3.04

2.7

2.7

2.8

3.1

3.1

3.4

M3

3.4

3.4

3.58

3.2

3.2

3.32

3.6

3.6

3.9

M4

4.5

4.5

4.68

4.3

4.3

4.42

4.8

4.8

5.1

M5

5.5

5.5

5.68

5.3

5.3

5.42

5.8

5.8

6.1

M6

6.6

6.6

6.82

6.4

6.4

6.55

7

7

7.36

M8

9

9

9.22

8.4

8.4

8.55

10

10

10.36

M10

11

11

11.27

10.5

10.5

10.68

12

12

12.43

Clearance hole chart for inch fasteners.

Nominal Screw Size

Fit Class - Normal

Fit Class - Close

Fit Class - Loose

Drill Size

Min CH

Max CH

Drill Size

Min CH

Max CH

Drill Size

Min CH

Max CH

#0

#48

0.076

0.082

#51

0.067

0.071

3/32

0.094

0.104

#1

#43

0.089

0.095

#46

0.081

0.085

#37

0.104

0.114

#2

#38

0.102

0.108

3/32

0.094

0.098

#32

0.116

0.126

#3

#32

0.116

0.122

#36

0.106

0.110

#30

0.128

0.140

#4

#30

0.128

0.135

#31

0.120

0.124

#27

0.144

0.156

#5

5/32

0.156

0.163

9/64

0.141

0.146

11/64

0.172

0.184

#6

#18

0.170

0.177

#23

0.154

0.159

#13

0.185

0.197

#8

#9

0.196

0.203

#15

0.180

0.185

#3

0.213

0.225

#10

#2

0.221

0.228

#5

0.206

0.211

B

0.238

0.250

1/4

9/32

0.281

0.290

17/64

0.266

0.272

19/64

0.297

0.311

🙋 This calculator provides an estimation of the clearance hole of fasteners, and the results are more likely to be in the fit class "loose". For exact values, you can use the ASME B18.2.8 charts.

FAQs

How do I calculate clearance hole?

To calculate a bolt or a screw clearance hole CH, you need to follow the steps below:

  1. Determine the diameter of the screw D.

  2. Determine the diameter of the screw head DH.

  3. Use the following:

    CH = (D + DH) / 2

  4. That's it! You can check your result with our clearance hole calculator.

What is the difference between bolt and screw?

The main difference between a bolt and a screw is that bolts are usually used to secure items in place, tightening and holding by use of a threaded nut. Bolts are often used for construction, building, or anchoring items. On the other hand, screws are commonly used to connect two objects together, being fully inserted into the object. Screws are often used in home repairs, DIY builds, and furniture.

What is the bolt clearance hole for a M8?

10.5 mm. The M8 bolt has a diameter D of 8 mm and a head diameter DH of 13 mm. The bolt clearance hole CH is calculated using the formula:

CH = (D + DH) / 2
CH = (8 mm + 13 mm) / 2
CH = 21 mm / 2
CH = 10.5 mm

Or, use our calculator to save your time.

What is the clearance hole for a 6-32 screw?

0.204". The 6-32 screw has a diameter D of 0.1380" and a head diameter DH of 0.270". The screw clearance hole is calculated as below:

CH = (D + DH) / 2
CH = (0.1380" + 0.270") / 2
CH = 0.408 / 2
CH = 0.204"

You can check this result with our calculator.

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