Convert inches to millimeters

Enter the number of inches you want to convert to millimeters in the text box below. The conversion to length in millimeters will update as you type.

Answer: 25.4
inches (in)
{"answerString":"25.4","answerSymbol":"millimeters"}
1 inches = 25.4 millimeters

Precise decimal and fraction answers

The conversion in millimeters rounded to six significant decimal places is 1 in = 25.400000 mm. The precise fraction answer is 25 2/5 mm.

Decimal Precision

Conversion from one to ten decimal places

  • 1 in = 25.4 mm
  • 1 in = 25.40 mm
  • 1 in = 25.400 mm
  • 1 in = 25.4000 mm
  • 1 in = 25.40000 mm
  • 1 in = 25.400000 mm
  • 1 in = 25.4000000 mm
  • 1 in = 25.40000000 mm
  • 1 in = 25.400000000 mm
  • 1 in = 25.4000000000 mm

How many millimeters are in an inch?

There are 25.4 millimeters in one inch. An inch is 25.4 times longer than a millimeter. A millimeter is 3.94% of a inch

Inches to millimeters conversion factor and formulas

Formula

The conversion factor between inches and millimeters is 25.4. This represents the ratio of millimeters per one inch. To calculate the value in millimeters, we can either multiply by the conversion factor or divide by its inverse.

Multiplication

To convert from inches to millimeters, multiply inches by 25.4.
The formula is expressed as:
in × 25.4 = mm

Division

Alternatively we can divide by the inverse conversion factor to get the same result.
The inverse of 25.4 is 1/25.4 or 0.039. To convert from inches to millimeters, divide inches by 0.039.
The formula is expressed as:
in ÷ 0.039 = mm

About this conversion

Converting inches to millimeters is a conversion between units from separate unit systems - inches are US Customary / UK Imperial defined units while millimeters are metric (SI) .

About Inches

Customary/Imperial Unit

The inch is a length measurement within US Customary and British Imperial units of measure. It is officially defined as 25.4 millimeters. Twelve inches equal one foot and thirty six inches equal a yard in the US/Imperial systems. The abbreviation for inches is either in or " as in 12". When measuring in inches, it is common to subdivide the inch into fractional portions like a half-inch, quarter-inch, eighth of an inch etc. instead of using decimals. Inches are frequently used in the building construction trades in the US and Canada. Internationally, inches are a common measurement of tire size and display screen sizes. Historically the inch is derived from the width of an adult thumb.

About Millimeters

SI Unit

Within the SI (metric) system of measurement, the millimeter is officially defined as one thousandth (1/1,000) of a meter. It is commonly used when measuring very short lengths. Internationally it is spelled 'millimetre' whereas the U.S. spells it 'millimeter'. The symbol for millimeters is mm.

Reverse this conversion

Convert from millimeters to inches instead.

1 inches to other length units

Metric

  • 1 in = 2.54×10-5 km
  • 1 in = 0.025 m
  • 1 in = 0.254 dm
  • 1 in = 2.54 cm
  • 1 in = 25.4 mm
  • 1 in = 25,400 µ
  • 1 in = 2.54×107 nm

Imperial/U.S.

  • 1 in = 1.578×10-5 mi
  • 1 in = 0.028 yd
  • 1 in = 0.083 ft
  • 1 in = 1 in

References and Citations

  1. National Institute of Standards and Technology (NIST) General Tables of Units of Measurement
  2. International Bureau of Weights and Measures (BIPM) The International System of Units (SI)

Inches to millimeters conversion table

in mm
1 in 25.4 mm
2 in 50.8 mm
3 in 76.2 mm
4 in 101.6 mm
5 in 127 mm
6 in 152.4 mm
7 in 177.8 mm
8 in 203.2 mm
9 in 228.6 mm
10 in 254 mm
in mm
20 in 508 mm
30 in 762 mm
40 in 1,016 mm
50 in 1,270 mm
60 in 1,524 mm
70 in 1,778 mm
80 in 2,032 mm
90 in 2,286 mm
100 in 2,540 mm
1,000 in 25,400 mm

More in to mm conversions

Frequent conversions from inches

in to ft in to yd in to mm in to cm in to m