Millimeter (mm) and inch (in) are common units of length used in engineering, manufacturing, and everyday life.
What is a millimeter?
A millimeter is one‑thousandth of a meter. It is part of the metric system and is widely used for precise measurements in machining, medical devices, and CAD drawings.
What is an inch?
An inch is defined as exactly 25.4 millimeters. It belongs to the Imperial/US customary system and appears in automotive, aerospace, and construction specifications.
Why convert between them?
Global collaboration often requires translating designs from metric to Imperial units and vice‑versa. The conversion factor is:
\\(1\\text{ mm}=0.03937007874015748\\text{ in}\\)
\\(1\\text{ in}=25.4\\text{ mm}\\)
Using this factor ensures dimensional accuracy when parts are manufactured in different regions.
Millimeter to Inch Conversion Reference Table
Millimeter (mm)
Inch (in)
0.1
0.0039
0.5
0.0197
1.0
0.0394
2.0
0.0787
5.0
0.1969
10.0
0.3937
20.0
0.7874
50.0
1.9685
100.0
3.937
500.0
19.685
1000.0
39.3701
Convert 10 mm to inches:
Write the known factor: \\(1\\text{ mm}=0.03937007874015748\\text{ in}\\).
Rounded to three decimal places, 10 mm ≈ 0.394 in.
The exact conversion is given by the factor \(1\text{ mm}=0.03937007874015748\text{ in}\). Multiplying 1 mm by this factor yields 0.03937007874015748 in.
Use the full conversion constant (0.03937007874015748) in calculations and only round the final result. In spreadsheets or scripts, store the factor as a double‑precision number and apply it to each value before any rounding.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)