The inch (in) is a US customary and imperial unit of length. NIST gives it as exactly 0.0254 meters, which is 2.54 cm or 25.4 mm. Twelve inches make a foot and 36 inches a yard.
Conversion
cm = in × 2.54
mm = in × 25.4
in = m × 39.3701
Example
A 30 cm ruler is 30 ÷ 2.54 = 11.81 in. A 1 m length is 1 ÷ 0.0254 = 39.37 in, which is 3 ft 3.37 in. A 6 ft pole is 72 in, or 182.88 cm.
The guide how to read a tape measure explains inch fractions, and how many feet in a meter shows inch conversions for heights. The converters mm to inches and meters to inches take any value.
Common mistakes
Fractions of an inch are not decimals: 5/8 in is 0.625 in (15.9 mm), not 0.58. Convert fractions by dividing, then multiply by 25.4 for millimeters.