Convert millimeter to fractional inches and inches to mm

just type a value, mm values just numbers and fractional inches values should include slash ( / ) or ( " )


How use this conversion calculator?

convert millimeters (mm) to fractional inches - decimal inches to millimeters mm calculator

mm to in   millimeter to fractional inches

just enter the metric (mm) value and choose the divisor i.e.:

  9.5   mm   in divisor 16
      0 5/16″   7.9375 mm
      0 3/8″   9.5250 mm

in to mm   decimal inch to fraction of inch and millimeter

enter the value using double prime (″), i.e.:

  1.25″ dec. inch   divisor 16
      1 1/4″   31.7500 mm

To improve the approximation in fractional inches, set 512 in the divisor.

in to mm   fraction of inches to millimeter

enter value with slash (/), i.e.:

  1/8 frac. inches   divisor 64
      1/8″   3.1750 mm

enter value with space and slash (/), i.e.:

  1 1/4 frac. inches   divisor 16
      1 3/4″   44.4500 mm

or enter the value using ( " ), space or slash ( / ), i.e.:

  1″ 3/8 frac. inches   divisor 16
     1 3/8″   34.9250 mm

mistakes, typos or crazy values are rounded to the best approximation, i.e.:

  2 3/83 frac. inches   divisor 128
     2 1/32″   51.5938 mm
     2 5/128″   51.7922 mm

caculator to convert mm in fraction of inches and inches to mm - decimal inches to mllimeters (mm)


In practical terms it is rare to find denominators greater than 64. In these cases, the thousandth inch measurements "thousand" or "thou" (invented by Whitworth, the same as the threads) are more used and are equivalent to 1"/1000
    thousandth > thou (UK)
    mille > mil (USA)
even smaller:
    tenths = thou / 10 = 0.0025 mm = 2.5 ┬Ám µm

The Metric System

The Metric System was officially created in France in 1790. By the advantages it has been adopted by many countries, currently only a few do not, which facilitates scientific work and trade relations.
The Metric System uses 10 as divisor and the Imperial System uses 12 divisible by 2, 3, 4 and 6. In our daily lives is common the use of such fractions ( 1/4 pound, 3/4 gallon ...) as well as the use of some units such as the gallon in chemicals (1/4 = 900 mL), gold in ounces, construction steel gauges, tire sizes ( 14″ ), many screws are still marketed in inch and even the screens of televisions and phones released in inches.

Like other systems, the "Imperial" had some slight variations between the adopted standards, i.e.: an inch in England was not exactly the same as a Canadian inch and the Imperial gallon differed from the American gallon, these and other differences generated numerous technical-commercial problems. It was not until the late 1950s that the Imperial System was uniformed worldwide, and among other resolutions, the equivalence between millimeter and inch was established:

25.4 mm = 1 in ( inch )