Convert mm to inches
Convert mm to inches instantly. 1 mm = 0.03937 in. Formula, worked examples and a quick reference table.
Last updated
One millimeter equals 0.03937 inches. To convert any number of millimeters to inches, multiply by 0.03937008.
The converter above works in both directions and updates as you type. Below you will find the formula, a worked example and a reference table of common values.
Length conversions come up wherever a measurement crosses a border: a height given in feet and inches on a form that wants centimetres, a running distance recorded in kilometres and compared against miles, a component specified in millimetres and ordered from a supplier working in inches. The conversions themselves are exact — the inch, foot, yard and mile have all been defined in metric terms since 1959 — so any discrepancy comes from rounding, not from the units disagreeing.
mm to inches formula
To go the other way, use millimeter = inch ÷ 0.03937008.
About these units
The millimetre is the working unit of engineering drawings and machining across most of the world, precise enough that dimensions rarely need decimals.
The inch has been defined as exactly 25.4 millimetres since the 1959 international yard and pound agreement, which finally reconciled slightly different British and American definitions.
Millimeter is also written millimetre, millimetres and millimeters. Inch is also written inches and ".
Sources
mm to inches conversion table
| Millimeter | Inch |
|---|---|
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.1181 in |
| 5 mm | 0.1969 in |
| 10 mm | 0.3937 in |
| 20 mm | 0.7874 in |
| 25 mm | 0.9843 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.937 in |
| 250 mm | 9.8425 in |
| 500 mm | 19.685 in |
| 1,000 mm | 39.3701 in |
Frequently asked questions
How many inches are in a millimeter? +
There are 0.03937 inches in one millimeter.
What is 10 mm in in? +
10 mm equals 0.3937 in. Multiply 10 by 0.03937008.
How do I convert inch back to millimeter? +
Use millimeter = inch ÷ 0.03937008. The converter above handles both directions, or see our dedicated inches to mm page.
How accurate is this millimeter to inch conversion? +
The factor used is 0.0393700787, carried at full double precision. Where a unit has an exact legal definition the factor is exact rather than approximate. Rounding is applied only to the displayed result, so the answer is never a calculation done on an already-rounded number.
Is there a quick way to estimate mm to in in my head? +
Divide by 25.4. That reproduces the exact factor of 0.03937 to the precision you could read off a result anyway.