1 inch in millimeters

Conversion

1 inch is equivalent to 25.4 millimeters.^[1]

Conversion in the opposite direction

The inverse of the conversion factor is that 1 millimeter is equal to 0.0393700787401575 times 1 inch.

It can also be expressed as: 1 inch is equal to $\frac{1}{0.0393700787401575}$ millimeters.

Approximation

An approximate numerical result would be: one inch is about zero millimeters, or alternatively, a millimeter is about zero point zero four times one inch.

Units involved

This is how the units in this conversion are defined:

Inches

The inch (abbreviation: in or ″) is a unit of length in the imperial and United States customary systems of measurement now formally equal to 1⁄36 yard but usually understood as 1⁄12 of a foot. Derived from the Roman uncia (twelfth), inch is also sometimes used to translate related units in other measurement systems, usually understood as deriving from the width of the human thumb. Traditional standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as exactly 2.54 cm.

Wikipedia page of inches

Millimeters

The millimetre or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length.

Wikipedia page of millimeters

Footnotes

[1] The precision is 15 significant digits (fourteen digits to the right of the decimal point).

Results may contain small errors due to the use of floating point arithmetic.