Convert Millimeter to Inch (mm → in)

The millimeter is the precision unit used in engineering, manufacturing, and weather rainfall reports.

Millimeter

Inch

0.03937

1 mm0.03937 inNIST · BIPM accuracy

Millimeter to Inch Conversion Table

10 common values

Millimeter	Inch
1 mm	0.03937 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
250 mm	9.84252 in
500 mm	19.685039 in
1,000 mm	39.370079 in
5,000 mm	196.85039 in

How to Convert Millimeter to Inch Manually

Step by Step

Converting millimeters to inches is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1
Take your value in millimeters
Start with the number of millimeters (mm) you want to convert.
2
Multiply by 0.03937
The conversion factor from mm to in is 0.03937. Multiply your value by this number.
3
Read the result in inches
The result is your value in inches (in).

Practical Examples

1 mm

equals

0.03937 in

5 mm

equals

0.19685 in

10 mm

equals

0.393701 in

25 mm

equals

0.984252 in

100 mm

equals

3.937008 in

Formula

Multiply the value in millimeters by 0.03937. For the reverse direction, multiply by 25.4.

Forwardin = mm × 0.03937

Reversemm = in × 25.4

Example: 10 mm × 0.03937 = 0.393701 in

Tips

Use these in everyday conversions

1 mm is the smallest graduation on a standard ruler. 10 mm = 1 cm exactly.
Rainfall in mm is depth — 25 mm of rain over 1 m² equals 25 litres of water.
For very small measurements switch to micrometres (µm) — 1 mm = 1000 µm.

Common Mistakes

Avoid these

Reading an engineering drawing dimensioned in mm as if it were cm — a factor-of-10 error.
Using 25 instead of 25.4 when converting mm to inches — the error matters in CNC machining.
Confusing millimetre (length) with millilitre (volume) — both abbreviated with "ml" but on different scales.

About Millimeter and Inch

What is the Millimeter?

The millimeter equals one thousandth of a meter (0.001 m) and is the precision unit of choice in engineering, manufacturing, electronics, and meteorology. Its small size makes it ideal for tolerances in mechanical parts, paper thickness, and rainfall measurements. A standard credit card is 0.76 mm thick, and a sheet of office paper is about 0.1 mm. The millimeter is the universal unit for tire-tread depth, weather-station rainfall reports, and 3D printer resolution. It relates to the centimeter (10 mm = 1 cm), the inch (25.4 mm = 1 in exactly), and the micrometer (1 mm = 1,000 µm). Engineering drawings worldwide default to millimeters for dimensions, except in the United States where inches remain dominant in mechanical engineering.

Rainfall measurements in weather reports
Precision engineering and manufacturing tolerances
Medical imaging — tumor and wound size

Real-world examples

A 2 euro coin is 25.75 mm across and 2.2 mm thick. Rainfall of 50 mm in 24 h is a red-warning event in most of Europe.

What is the Inch?

The inch equals exactly 25.4 millimeters under the 1959 international yard and pound agreement. The word derives from the Old English 'ynce,' from Latin 'uncia' meaning one twelfth (the inch is one twelfth of a foot). Originally based on the width of a thumb, the inch has been standardized for centuries. It is the global standard for screen sizes (a 15-inch laptop or 65-inch TV), pipe and tubing diameters (1-inch plumbing, 2-inch exhaust), and shoe sizes in Anglo-Saxon countries. Construction lumber, photographic prints, paper sizes (US Letter is 8.5 × 11 in), and rainfall in the US all use inches. The inch relates to the millimeter (25.4 mm = 1 in exactly), the foot (12 in = 1 ft), and the yard (36 in = 1 yd). Subdivisions in fractions (½, ¼, ⅛) remain common in carpentry.