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When you need to measure length and switch between different systems of measurement—like the metric system (using millimeters) and the imperial system (using inches)—a simple formula is all you need.
To convert millimeters to inches, the most important number to know is 0.03937.
The formula is:
Inches = Millimeters × 0.03937
This single step is the fastest way to convert mm to inches.
For example, if you have a measurement of 10mm, you would multiply it by 0.03937 to get 0.3937 inches.
Here are some quick reference conversions from Millimeter (mm) to Inch (in):
| Millimeters | Inches |
|---|---|
| 0.000001 mm | in |
| 0.001 mm | in |
| 0.1 mm | in |
| 1 mm | in |
| 2 mm | in |
| 3 mm | in |
| 4 mm | in |
| 5 mm | in |
| 6 mm | in |
| 7 mm | in |
| 8 mm | in |
| 9 mm | in |
| 10 mm | in |
| 20 mm | in |
| 30 mm | in |
| 40 mm | in |
| 50 mm | in |
| 100 mm | in |
| 1000 mm | in |
| 10000 mm | in |
For all Length converters, choose units using the From/To dropdowns above.
A millimeter (mm) is a small unit of length in the metric system, equal to one-thousandth of a meter (1/1000 m or 0.001 m).
The word itself comes from the Latin "mille," meaning "thousand."
This is why the prefix "milli" in the metric system always means one-thousandth of a base unit—just like a milligram is one-thousandth of a gram.
The plural form is millimeters.
Understanding the relationship between millimeters and inches is crucial, particularly for projects that utilize both metric and imperial systems.
The official mm-to-inch conversion is a precise measurement used worldwide in engineering and manufacturing.
The millimeter is the standard unit for measuring small distances with precision.
You likely encounter millimeter measurements more often than you think in daily life, science, and technology.
An inch (in) is a standard unit of length used in the imperial and United States customary systems.
It is most commonly known as 1/12 of a foot. The plural form is "inches."
For a quick inch definition, here are the most important conversions:
The history of the inch goes back centuries. The word "inch" itself originates from the Latin word uncia, meaning "one-twelfth," which highlights its relationship to the larger unit of a foot.
Early definitions were often based on natural reference points. For a long time, an inch was widely considered to be the width of a man's thumb at the base of the nail.
To create a more reliable standard, 14th-century English King Edward II officially defined the inch as the length of three grains of barley placed end to end.
While the inch is an imperial unit, its official modern definition is based on the metric system.
Since 1959, an international agreement has defined the inch as exactly 2.54 centimeters (or 25.4 millimeters).
This universal standard, agreed upon by the United States, the United Kingdom, and other nations, ensures that the inch has a precise and globally recognized value.
This consistency is crucial for international trade, engineering, and science.
In fields that require extreme accuracy, such as engineering and machining, the inch is often divided into even smaller parts.
One-thousandth of an inch (1/1000 or 0.001 inches) is commonly known as a "thou" or a "mil."
Although very small, this unit is crucial for defining tolerances in the manufacture of engine components, electronic devices, and other precision equipment, where minute differences can have significant effects.
By comparison, a standard piece of paper measures roughly 2–4 thou in thickness.