Millimeters to Inches Converter
Convert mm to inches, with the nearest tape-measure fraction and how far off it is.
Divide millimeters by 25.4 to get inches, because an inch is exactly 25.4 mm. So 50 mm is 1.9685 in. On a tape measure marked in 16ths, the nearest mark is 1 15/16 in, which is 0.79 mm short of 50 mm. One millimeter is about 0.03937 in.
This converter uses the exact definition of the inch, so the decimal answer is exact apart from display rounding. The fraction is rounded to the nearest mark you choose; for machining or fit-critical work, check the tolerance against the decimal value.
In inches
1.9685 in
- Nearest 16th
- 1 15/16 in (0.79 mm short of exact)
- Feet and inches
- 0 ft 1.9685 in
- Centimeters
- 5 cm
Inches = millimeters / 25.4, exactly.
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About the MM to Inches Converter
The inch has been defined as exactly 25.4 millimeters since 1959, and NIST lists the factor as exactly 0.0254 meter per inch, so every mm to inches answer here is one division by 25.4. A 10 mm bolt is 0.3937 in and a 100 mm board is 3.9370 in. Rulers and tape measures in the US mark fractions rather than decimals, usually down to 16ths, so the converter also rounds to the nearest mark you choose, from halves to 64ths, and says how many millimeters that mark is short or long. A 16th of an inch is about 1.59 mm, so a 16ths answer is never more than about 0.79 mm off; pick 32nds or 64ths for finer work. Feet and inches split the length into 12-inch feet and the inches left over, and the centimeter figure is the millimeters divided by 10.
Frequently asked questions
How many millimeters are in an inch?+
Exactly 25.4. The international inch was fixed at 25.4 mm in 1959, so converting mm to inches is a division by 25.4, exact before display rounding.
What is 10 mm in inches as a fraction?+
10 mm is 0.3937 in. The nearest 16th is 3/8 in (6/16), which is about 0.48 mm short; the nearest 32nd is 13/32 in, which is about 0.32 mm long.
How do I read a millimeter length on an inch tape measure?+
Convert it here with the fraction set to your tape's smallest mark, usually 1/16 in, then find that whole inch and fraction on the tape. The result row shows how many millimeters the mark is short or long of the exact length.
Can I convert inches back to millimeters?+
Multiply inches by 25.4. For a fraction, divide first: 3/8 in is 0.375 in, and 0.375 times 25.4 is 9.525 mm.
How many mm is 1/4 inch?+
1/4 in is 0.25 in, and 0.25 times 25.4 is 6.35 mm, exactly.
Conversion factor of 1 inch = 2.54 E-02 meter (25.4 mm), exact: National Institute of Standards and Technology, Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8, Factors for Units Listed Alphabetically. Feet and inches use 12 inches in a foot.
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