Inches to millimetres conversion chart - Thread diameter chart

Inch to MM Converter

Conversion of inches to millimetres

One inch equals exactly 25.4 millimetres. This value is fixed, making it a reliable standard for conversions.

However, take into account that the conversion factor does not apply to pipe threads, which have completely different dimensions.

How to convert inches into millimetres?

To convert inches to millimetres, all you need to do is multiply the number of inches by 25.4. For example:

2 inches = 2 x 25.4 = 50.8 mm

5 inches = 5 x 25.4 = 127 mm

Inch to millimetre converter

How to convert millimetres into inches?

The reverse conversion, i.e. from millimetres to inches, requires dividing the number of millimetres by 25.4. For example:

50 mm = 50 / 25.4 ≈ 1.97 inches

100 mm = 100 / 25.4 ≈ 3.94 inches

Millimetre to Inch converter

Inches to millimetres conversion chart - Table of thread diameters in inches per mm

Inches Millimeters
1/32 0.79
1/16 1.59
3/32 2.38
1/8 3.17
5/32 3.97
3/16 4.76
7/32 5.56
1/4 6.35
9/32 7.14
5/16 7.94
11/32 8.73
3/8 9.53
13/32 10.32
7/16 11.11
15/32 11.91
1/2 12.70
17/32 13.49
9/16 14.29
19/32 15.08
5/8 15.88
21/32 16.67
11/16 17.46
23/32 18.26
3/4 19.05
25/32 19.84
13/16 20.64
27/32 21.43
7/8 22.23
29/32 23.02
15/16 23.81
31/32 24.61
1 25.40
1 1/8 28.575
1 1/4 (5/4) 31.75 (32)
1 3/8 34.925
1 1/2 (6/4) 38.1
1 5/8 41.275
1 3/4 44.45
1 7/8 47.625
2 50.8
2 1/4 57.15
2 1/2 63.5
2 3/4 69.85
3 76.2
3 1/4 82.55
3 1/2 88.9
3 3/4 95.25
4 101.6
5 127.0
6 152.4

What is an inch?

The inch is a traditional unit of length, widely used in countries that use the imperial system of measurement, such as the United States and the United Kingdom. It also appears in many specialised applications around the world.

The origins of an inch date back to times before the 10th century when it was defined in various ways, usually as the width of a thumb or three barleycorns placed next to each other The modern definition of an inch as 25.4 millimeters was established in 1959 to standardize international measurement standards.

When do inches get used to measure threads?

Inches are used to measure threads primarily in countries using the imperial system of measurement. However, they are also used in Europe when dealing with inch threads. They are characterised by an outline angle of 60° or 55° and a thread pitch described as the number of turns per inch (TPI).

What is the millimetre?

The millimetre is the basic unit of measurement in the metric system, widely used throughout the world in a variety of applications, from engineering to everyday life. It is equal to one thousandth of a metre.

When are millimetres used to measure threads?

Millimetres are used to measure threads when we are dealing with threads in the metric system. They differ from inch threads primarily in terms of thread pitch, which in this case is described as the distance between adjacent coils (expressed in millimetres).

Recall that in the imperial system, thread pitch refers to the number of coils per inch.

How to read the dimensions of metric threads?

To read the dimensions of metric threads, you need to look at their designation. Metric threads are designated as M followed by a number indicating the diameter in millimetres, e.g. M8 is a metric thread with a diameter of 8 millimetres . Often the thread pitch is also given, for example M8 x 1.25, where 1.25 is the thread pitch (also in millimetres).

How to read the dimensions of inch threads?

To read the dimensions of inch threads you need to look at what designation they have. Inch threads are designated by their diameter in inches followed by the number of coils per inch, e.g. 1/2"-20, where 1/2 inch is the diameter and 20 is the number of coils per inch.

Thread dimensions chart

How to measure a thread in inches?

To measure the thread in inches, follow the steps below:

  1. Measure the diameter - Use a calliper to measure the diameter of the thread. Read off the result in inches. 
  2. Determine the number of coils per inch - Use a thread gauge to check the pitch of the thread. To do this, match the appropriate tool template to the thread coils and read the size shown on the template. (Alternatively, you can use a calliper to determine 1 inch and count the coils yourself). 
  3. Read the dimensions - Combine the previous data to get the full dimensions of the thread, e.g. 1/2"-20, which means a thread with a diameter of 1/2 inch and 20 coils per inch.

How to measure a thread in millimetres?

To measure a thread in millimetres, follow the steps below:

  1. Measure the diameter - Use a calliper to measure the diameter of the thread in millimetres. 
  2. Determine the thread pitch - Use a metric thread gauge to measure the distance between the thread pitches. Read the result from the gauge and you will know the thread pitch in millimetres. (Alternatively, you can use a calliper to measure, for example, 1 cm of thread. Then divide the number of coils it contains by 10 and you will get the pitch in mm).
  3. Read the dimensions - Combine the data to get the full dimensions of the thread, e.g. M8 x 1.25, which means a thread with a diameter of 8 mm and a pitch of 1.25 mm.
How to measure a thread
Photo of Bartosz Kułakowski - CEO of Hosetech sp. z o. o.

Articles author

Bartosz Kułakowski

CEO of Hosetech Sp. z o.o.

Bartosz Kulakowski is an industrial hoses and couplings specialist with over 10 years of experience. Bartosz has been present in the technical industry since 2013. He gained experience as a technical and commercial advisor in the sector of plastic conveyor belts, steel structures, industrial hoses, and connectors. Since 2016, he has specialized exclusively in hoses and connectors. In 2019 he opened his own business under the HOSETECH Bartosz Kulakowski brand and since July 2022 he has been the CEO of the capital company HOSETECH Sp z o. o. (LLC).

SPIS TREŚCI

Conversion of inches to millimetres

How to convert inches into millimetres?

How to convert millimetres into inches?

Inches to millimetres conversion chart - Table of thread diameters in inches per mm

What is an inch?

When do inches get used to measure threads?

What is the millimetre?

When are millimetres used to measure threads?

How to read the dimensions of metric threads?

How to read the dimensions of inch threads?

How to measure a thread in inches?

How to measure a thread in millimetres?

;