in to mm Conversion Calculator
Click on the following link if you want to convert millimeters to inches – mm to in
History
The inch (in) is an ancient unit of length that dates back to the early Middle Ages and was originally based on the width of a man’s thumb. It became standardized in 1959 when the international inch was officially defined as exactly 25.4 millimeters.
The millimeter (mm), on the other hand, is a metric unit developed in France in the late 18th century as part of the metric system. It’s now the global standard for small and precise measurements.
Because the metric system is decimal-based, converting between millimeters and other metric units (like centimeters and meters) is very straightforward.
Common Usage
- Inches (in) are mainly used in the United States, Canada, and the UK for construction, screen sizes, and personal height.
- Millimeters (mm) are used worldwide in engineering, manufacturing, design, and science.
For example, a 24-inch monitor has a diagonal length of about 610 mm.
Inches to Millimeters Conversion Formula
The conversion between inches and millimeters is exact:
mm = in × 25.4
Example:
Convert 5 inches to millimeters.
5 × 25.4 = 127 mm
So, 5 inches equals exactly 127 millimeters.
Conversion Table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127.0 mm |
| 10 in | 254.0 mm |
| 15 in | 381.0 mm |
| 20 in | 508.0 mm |
| 25 in | 635.0 mm |
| 30 in | 762.0 mm |
| 40 in | 1,016.0 mm |
| 50 in | 1,270.0 mm |
Fun Facts
- 1 inch = 25.4 mm is one of the most precise and globally agreed-upon conversion values.
- The diameter of a U.S. quarter coin is almost exactly 1 inch (24.26 mm).
- The paper thickness of a standard office sheet is about 0.1 mm — so 1 inch equals roughly 250 sheets stacked together.
Frequently Asked Questions
1. How many millimeters are in one inch?
Exactly 25.4 mm.
2. Why was 25.4 mm chosen as the standard?
It was defined in 1959 by international agreement for consistent conversions between imperial and metric systems.
3. Where are inches still used?
Inches are commonly used in the U.S., UK, and Canada, especially for construction, tools, and screens.
4. How do I quickly estimate inches in mm?
Multiply by 25 for a rough mental calculation.
5. How do I convert mm back to inches?
Divide millimeters by 25.4.
