What is 1 inch equal to in mm?

›› More information from the unit converter

How many inch in 1 mm? The answer is 0.039370078740157.
We assume you are converting between inch and millimetre. You can view more details on each measurement unit:

inch or mm

Type in your own numbers in the form to convert the units!

1 inch to mm = 25.4 mm

2 inch to mm = 50.8 mm

3 inch to mm = 76.2 mm

4 inch to mm = 101.6 mm

5 inch to mm = 127 mm

6 inch to mm = 152.4 mm

7 inch to mm = 177.8 mm

8 inch to mm = 203.2 mm

9 inch to mm = 228.6 mm

10 inch to mm = 254 mm

You can do the reverse unit conversion from mm to inch, or enter any two units below:

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inch to Scots foot
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inch to hair's breadth

›› Definition: Inch

An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot. The inch is usually the universal unit of measurement in the United States, and is widely used in the United Kingdom, and Canada, despite the introduction of metric to the latter two in the 1960s and 1970s, respectively. The inch is still commonly used informally, although somewhat less, in other Commonwealth nations such as Australia; an example being the long standing tradition of measuring the height of newborn children in inches rather than centimetres. The international inch is defined to be equal to 25.4 millimeters.

›› Definition: Millimeter

A millimetre (American spelling: millimeter, symbol mm) is one thousandth of a metre, which is the International System of Units (SI) base unit of length. The millimetre is part of a metric system. A corresponding unit of area is the square millimetre and a corresponding unit of volume is the cubic millimetre.

›› Metric conversions and more

ConvertUnits.com provides an online conversion calculator for all types of measurement units. You can find metric conversion tables for SI units, as well as English units, currency, and other data. Type in unit symbols, abbreviations, or full names for units of length, area, mass, pressure, and other types. Examples include mm, inch, 100 kg, US fluid ounce, 6'3", 10 stone 4, cubic cm, metres squared, grams, moles, feet per second, and many more!

An inch is a unit of length or distance in a number of systems of measurement, including in the US Customary Units and British Imperial Units. One inch is defined as 1⁄12 of a foot and is therefore 1⁄36 of a yard. According to the modern definition, one inch is equal to 25.4 mm exactly.

A millimeter (mm) (mispeled millimeter) is a decimal fraction of the meter, the International System of Units (SI) unit of length, approximately equivalent to 39.37 inches.

To calculate a value in inches to the corresponding value in millimeters, just multiply the quantity in inches by 25.4 (the conversion factor).

Value in millimeters = value in inches × 25.4

Supose you want to convert an inch into millimeters. In this case you will have:

Value in millimeters = 1 × 25.4 = 25.4

Note: Fractions are rounded to the nearest 8th fraction. Values are rounded to 4 significant figures.

Please provide values below to convert inch [in] to millimeter [mm], or vice versa.

Definition: An inch (symbol: in) is a unit of length in the imperial and US customary systems of measurement. An inch was defined to be equivalent to exactly 25.4 millimeters in 1959. There are 12 inches in a foot and 36 inches in a yard.

History/origin: The term "inch" was derived from the Latin unit "uncia" which equated to "one-twelfth" of a Roman foot.

There have been a number of different standards for the inch in the past, with the current definition being based on the international yard. One of the earliest definitions of the inch was based on barleycorns, where an inch was equal to the length of three grains of dry, round barley placed end-to-end. Another version of the inch is also believed to have been derived from the width of a human thumb, where the length was obtained from averaging the width of three thumbs: a small, a medium, and a large one.

Current use: The inch is mostly used in the United States, Canada, and the United Kingdom. It is also sometimes used in Japan (as well as other countries) in relation to electronic parts, like the size of display screens.

Millimeter

Definition: A millimeter (symbol: mm) is a unit of length in the International System of Units (SI). It is defined in terms of the meter, as 1/1000 of a meter, or the distance traveled by light in 1/299 792 458 000 of a second.

History/origin: The milli- prefix is one of many metric prefixes. It indicates one thousandth of the base unit, in this case the meter. The definition of the meter has changed over time, the current definition being based on the distance traveled by the speed of light in a given amount of time. The relationship between the meter and the millimeter is constant however. Prior to this definition, the meter was based on the length of a prototype meter bar. In 2019, the meter has been re-defined based on the changes made to the definition of a second.

1 in = 25.4 mm1 mm = 0.0393700787 in

Example: convert 15 in to mm:
15 in = 15 × 25.4 mm = 381 mm

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Share How many millimeters in an inch? 1 inch is equal to 25.4 millimeters, which is the conversion factor from inches to millimeters.

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An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. Its size can vary from system to system. There are 36 inches in a yard and 12 inches in a foot. A corresponding unit of area is the square inch and a corresponding unit of volume is the cubic inch. See all conversions for inches here.

A millimetre (American spelling: millimeter, symbol mm) is one thousandth of a metre (the metre is the International System of Units (SI) base unit of length). The millimetre is part of a metric system. The corresponding unit of area is the square millimetre and the corresponding unit of volume is the cubic millimetre. See all conversions for millimeters here.