Inches to Millimeters Converter

Use this converter to easily convert between Inches and Millimeters (in to mm).

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How many Millimeters equal one Inch?

Millimeters and Inches are measurement units of length. According to the International System of Units (SI) one inch is equal to exactly 25.4 millimeters, so 25.4 mm equal 1 inch. The international symbol for millimeters is mm, and for inches – in. The inch is also commonly depicted by double quotes ().

Difference between Inches and Millimeters

Both inches and millimeters are units that measure length, but they belong to different measurement systems. The inch is an imperial unit, whereas the millimeter is a metric unit.

According to historic texts, the inch was first recognized in the 7th century as a means of assessing wound depth. Its first official definition dates from 1324 – three grains of barley, dry and round, placed end to end, lengthwise. For a long time the inch was referred to as being equal to the width of an average person’s thumb. In 1930, the inch as a unit equal to 25.4 mm was adopted by the British Standards Institution. This so-called industrial inch was soon adopted by the US in 1933, and later on by 16 more countries.

Nowadays, it is mostly used in the US, the UK, Canada, and Japan. Throughout the world, the inch finds application in electronics – display screen sizes are measured in inches.

The millimeter is derived from the base measurement unit established by the SI – the meter. Its prefix ‘milli’ indicates that it is only 1/1,000 of a meter. Therefore, the mm can be defined as being equal to the path length that light travels in vacuum in 1/299,792,458,000 of a second. The millimeter is also equal to precisely 5/127 of an inch. In decimal that is approximately 0.03937.

The mm is used when performing tasks that require great precision, for example in mechanics, electronics or for scientific purposes.

Usually, on a ruler both of these units are featured on opposite sides.

How to convert Inches to Millimeters

Knowing the relationship between inches and millimeters is key to converting inches to millimeters:

in x 25.4 = mm.

Inches to mm conversion example

Sample task: convert 6 inches to millimeters. Solution:

in * 25.4 = mm
6 in * 25.40 = 152.40 mm
End result:
6 in is equal to 152.40 mm

in to mm conversion table

in to mm conversion table
in mm
1 in 25.40 mm
2 in 50.80 mm
3 in 76.20 mm
4 in 101.60 mm
5 in 127 mm
6 in 152.40 mm
7 in 177.80 mm
8 in 203.20 mm
9 in 228.60 mm
10 in 254 mm
20 in 508 mm
30 in 762 mm
40 in 1,016 mm
50 in 1,270 mm
60 in 1,524 mm
70 in 1,778 mm
80 in 2,032 mm
90 in 2,286 mm
100 in 2,540 mm
200 in 5,080 mm
300 in 7,620 mm
400 in 10,160 mm
500 in 12,700 mm
600 in 15,240 mm
700 in 17,780 mm
800 in 20,320 mm
900 in 22,860 mm
1,000 in 25,400 mm


[1] NIST Special Publication 330 (2008) - "The International System of Units (SI)", edited by Barry N.Taylor and Ambler Thompson

[2] International Organization for Standardization (1993). ISO Standards Handbook: Quantities and units (3rd edition). Geneva: ISO. ISBN 92-67-10185-4.

Cite this converter & page

If you'd like to cite this online converter resource and information as provided on the page, you can use the following citation:
Georgiev G.Z., "Inch to mm Converter", [online] Available at: URL [Accessed Date: 12 Jun, 2021].