Inches to Millimeters Converter

Convert inches to millimeters instantly.

Common length units

Inch (in)

Definition: An inch (symbol: in or ") is a unit of length in the imperial and US customary systems of measurement. Since 1959, one inch has been defined as exactly 25.4 millimeters. There are 12 inches in a foot and 36 inches in a yard.

History/origin: The word inch derives from the Latin uncia, meaning one-twelfth. Early definitions were based on natural references: the width of a human thumb or the length of three barleycorns placed end to end. The modern standardized definition was agreed upon internationally in 1959.

Current use: The inch remains in common use in the United States, Canada, and the United Kingdom, particularly for human height, screen sizes, and construction materials such as lumber and pipes.

Millimeter (mm)

Definition: The millimeter is a small metric length unit. Each mm is 0.001 meters, and 10 millimeters make one centimeter.

History/origin: Metric measurement made it easy to divide the meter into thousandths, giving builders, makers, and engineers a precise unit that avoids awkward fractions.

Current use: Mm is used for screws, product specs, machining, 3D printing, phone dimensions, rainfall, medical scans, jewelry sizes, and layout work where centimeters are too coarse.