Convert Length from Inch to Millimeter (in to mm)
Multiple conversions

Inch to Millimeter Conversion Formula

To convert from Inch (in) to Millimeter (mm), use the following formula:

With $\frac{1}{3.28084}$ is the ratio between the base units Meter (m) and Foot (ft).

Example

Let's convert 5 Inch (in) to Millimeter (mm).

Using the formula:

Therefore, 5 Inch (in) is equal to $126.99999593600013005$ Millimeter (mm).

What is an Inch?

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:

• 1 inch = 1/12 of a foot
• 1 inch = 2.54 centimeters (exactly)
• Symbol: in or "

Where Did the Inch Come From?

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.

How is an Inch Defined Today?

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.

How Are Inches Used for High-Precision Measurements?

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.

What is a Millimeter (mm)?

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.

How Many Millimeters are in an Inch?

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.

• Exact Conversion: 1 inch is equal to exactly 25.4 millimeters.
• Quick Reference: For a simple real-world comparison, 1 millimeter is about the thickness of a credit card.

Where are Millimeters Used Every Day?

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.

• Weather: Meteorologists measure daily rainfall in millimeters.
• Stationery: The lead in a mechanical pencil is measured by its diameter in millimeters (e.g., 0.5 mm or 0.7 mm).
• Electronics: Small components on circuit boards and common connectors, like the 3.5 mm headphone jack, are measured in millimeters.

What is the imperial system?

What is the metric system?

Inch to Millimeter Conversion Table

Here are some quick reference conversions from Inch (in) to Millimeter (mm):