Last updated: May 28, 2024

Clearance Hole Calculator

Q: How do I calculate clearance hole?

To calculate a bolt or a screw clearance hole CH , you need to follow the steps below: Determine the diameter of the screw D . Determine the diameter of the screw head DH . Use the following: CH = (D + DH) / 2 That's it! You can check your result with our clearance hole calculator.

Q: 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.

Q: 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.

Q: 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.

Created by Marinara Andrade do Nascimento Moura, PhD candidate

Marinara Andrade do Nascimento Moura

PhD candidate

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Marinara holds a master’s degree in Technology and is working on her PhD in Civil Engineering. She has always been interested in science and engineering, mostly because she is passionate about solving problems. She has published her articles in important scientific journals and international conferences as a researcher. She has experience teaching undergraduate students and believes that teaching is a perfect way to learn because the more we give, the more we have. In her free time, she loves to cook (and eat!), travel with her husband, and chat with her friends. See full profile

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Reviewed by Steven Wooding

Steven Wooding

Physicist holding a 1st class degree and a member of the Institute of Physics. Creator of the UK vaccine queue calculator, and featured in many publications, including The Sun, Daily Mail, Express, and Independent. Tenacious in researching answers to questions and has an affection for coding. Hobbies include cycling, walking, and birdwatching. You can find him on Twitter @OmniSteve. See full profile

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Table of contents

What is a clearance hole?Clearance hole formula How to use the clearance hole calculator: an example Clearance hole charts FAQs

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:

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

Determine the diameter of the screw D.
Determine the diameter of the screw head DH.
Use the following:

CH = (D + DH) / 2
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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