Millimeters to Inches
An instant millimeters-to-inches converter, with the formula and a reference table below.
| Millimeters | Inches |
|---|---|
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.11811 in |
| 5 mm | 0.19685 in |
| 10 mm | 0.393701 in |
| 25 mm | 0.984252 in |
| 50 mm | 1.968504 in |
| 100 mm | 3.937008 in |
How to use
- Enter a value in the Millimeters field.
- The Inches figure appears immediately — no button to press.
- Typing in the Inches field converts back to Millimeters the same way.
- Use the reference table for the values that come up most often.
Millimeters to Inches formula
The factor from millimeters to inches is 0.0393700787.
in = mm × 0.0393700787
Put another way, one millimeter is exactly 5/127 inches.
Why this factor: the millimeter and the inch are both defined against the meter, so dividing one definition by the other gives 0.0393700787 directly. Both definitions are set out in full below.
To go the other way, divide by 0.0393700787 — or use the Inches to Millimeters converter, which is the same calculation reversed.
Worked example
Start with 12 mm. Multiply by 0.0393700787 to get 0.472441 in.
12 mm × 0.0393700787 = 0.472441 in
The converter above does this for any value you type, in either direction.
What is a millimeter?
A millimeter is one thousandth of a meter — the working precision unit of manufacturing and construction.
Definition: Exactly 0.001 meter by SI prefix definition.
Where it is used: Engineering drawings, machining tolerances, timber and steel dimensions, rainfall totals.
What is an inch?
An inch is one twelfth of a foot, used for small dimensions and for screen and wheel sizes globally.
Definition: Exactly 25.4 millimeters since the 1959 International Yard and Pound Agreement — an exact, not approximate, relation.
Where it is used: Screen diagonals, pipe and fastener sizes, tire and wheel diameters, and print layout worldwide.
Millimeters vs Inches
The millimeter is a metric unit while the inch is an imperial unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many inches are in a millimeter?
One millimeter equals 0.0393700787 inches.
What is the formula to convert millimeters to inches?
Multiply the number of millimeters by 0.0393700787. To reverse it, divide by 0.0393700787 instead.
How do I convert inches back to millimeters?
Divide by 0.0393700787, which is the same as multiplying by 25.4.
How many inches are in 10 millimeters?
10 mm works out to 0.393701 in.
How is the millimeter defined?
Exactly 0.001 meter by SI prefix definition.