How to Convert mm to Inches? – With Some Interesting Facts

Two of the most common units of Length is Millimeter and Inch. Generally, we use the unit millimeter to measure lengths on a smaller scale. For the broader range, the unit Inch is more convenient to use. Given their wide uses, it would be at times essential to know how to convert mm to inches (millimeters to inches) and vice-versa.

Units are the standards for measurement of different physical quantities in physics and metrology. Measurement of the dimensions is very vital in all the branches of science including the applied one. Also in our daily life, some of the conversion formulae may come handy if we know those beforehand.


So if you know formula for converting mm to inches then it would be quite useful at times.

The abbreviation for millimeter is mm, and the acronym for Inch is in or ″.

Conversion calculator – How to convert mm to inches?

You can use the following conversion calculator to convert mm to inches. Just enter the value of length in mms in the entry field to get the corresponding inches value.

The formula to convert millimeter to inches

The conversion formula of the millimeters to inches is as follows:

1 mm= 0.0393701 in

Example: If you want to convert 15 mm to inches then you need to multiply it with the factor of 0.0393701.

15 mm = 15 × 0.0393701 in = 0.5905515 in

You can also remember 0.59 instead of the whole figure to easily calculate it in your mind (You will obtain an approximate value in that case).

The Formula to convert inch to millimeter

The inch to millimeter conversion formula is easier than the above one.

1 in = 25.4 mm

Example: If you want to convert 8 inches to mms then you need to multiply it by the factor of 25.4.

Using the formula to convert inch to the millimeter, we get

8 in=8×25.4 mm=203.2 mm

What is millimeter?

A millimeter is a unit of length in the metric system which is equal to one-thousandth of a meter. The meter is the base unit of length in SI.

So one meter is equal to one thousand millimeters. And one centimeter contains ten millimeters.

  • Origin – The origin of the millimeter is the Latin word mille
  • Usages – It is used worldwide for length measurements, especially in the countries which have undergone the metrication and where a smaller scale than the centimeter is required.
  • The symbol for millimeter is mm.
  • One millimeter = 1000micrometers or 1000000 nanometers.

What is inch?

An inch is a unit of length which is equal to 1⁄36 yard or 1⁄12 of a foot. British imperial and the United States customary systems of measurement widely use this unit.


The inch has various subdivisions, like halves, quarters, eighths, sixteenths, and other powers of two. It can also be divided into hundredths (in the caliber of firearms) or thousandths.

  • Origin – The origin of the word ‘inch’ is the old English word ‘ince’ (or ynce) which in turn has come from the Latin unit uncial.1 Uncia was equal to  “one-twelfth” of a Roman foot, or pes. 1 ince was equal to the breadth of the base of the nail of a man’s thumb.
  • Usages – It is mostly used in the United States, United Kingdom, and Canada. Sometimes the length measurement system of Japan (as well as other countries) uses it too.
  • The international standard symbol of the inch is in. In the traditional system, its symbol is a doubleprime (″).
  • Some other units related to Inch are-
  • US Survey inches Many European countries used to have this customary unit before the adoption of the metric system.
  • Continental inches Many European countries used to have this common unit before the adoption of the metric system.
  • Scottish inch1 Scottish inch was equal to 1.0016 imperial inches. This unit is now obsolete.

Quick lookup

10.04 Inch
20.08 Inch
30.12 Inch
40.16 Inch
50.20 Inch
60.24 Inch
70.28 Inch
80.31 Inch
90.35 Inch
100.39 Inch
501.97 Inches
1003.94 Inches

Now as you know conversion formulae, let’s also know some interesting facts about them.

Some lesser-known and exciting facts about mm and inches

  • The wavelength of the Microwaves with a frequency of 300 GHz is 1 mm.
  • The approximate width of a human hair is around 0.02 to 0.04 mm. It is also the smallest range of distances which the human eye can resolve.
  • The thickness of a sheet of paper is typically between 0.07 mm and 0.18 mm. And that of an ordinary copy or printer paper is approximately a tenth of a millimeter.
  • One Mickey (named after Mickey Mouse) is approximately equal to 0.1 mm, which is the length of the smallest detectable movement of a computer mouse.
  • One smoot (a not-so-well-known unit of length) is equal to seven inches.
  • A Pyramid inch was equal to 1.00106 British inches.
  • Initially, a yard was equal to the length of a man’s belt. In the 12th century, King Henry I of England fixed the measurement of the yard. He defined it as the distance from his nose to the thumb of his outstretched arm. And today the measurement is equal to 36 inches.
  • One of the oldest definitions of an inch was equal to the length of three grains of the round, dry barley placed end-to-end.
  • The length of an average man’s foot is 12 inches. Also, 1 foot=12 inches and that is why the unit ‘foot’ is called so.

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