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01 inch equals 25.4 millimeters (mm).
The inch is converted to millimeters by multiplying its value by 25.4, since one inch is exactly defined as 25.4 mm. This conversion is used widely in engineering, manufacturing, and everyday measurements.
Table of Contents
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is:
millimeters = inches × 25.4
This works because the inch is internationally defined as exactly 25.4 millimeters. When you multiply the number of inches by 25.4, you get the equivalent length in millimeters.
Example:
- Convert 1 inch to mm: 1 × 25.4 = 25.4 mm
- Convert 0.5 inch to mm: 0.5 × 25.4 = 12.7 mm
Conversion Example
- Convert 3 inches to mm:
- Start with 3 inches.
- Multiply by 25.4: 3 × 25.4 = 76.2 mm.
- Result: 3 inches equals 76.2 millimeters.
- Convert 0.75 inches to mm:
- Take 0.75 inches.
- Multiply by 25.4: 0.75 × 25.4 = 19.05 mm.
- So 0.75 inches is 19.05 millimeters.
- Convert 10 inches to mm:
- Start with 10 inches.
- Multiply by 25.4: 10 × 25.4 = 254 mm.
- Therefore, 10 inches equal 254 millimeters.
Conversion Chart
The chart below shows values from -24.0 inches to 26.0 inches, converted into millimeters. You can look up any inch value within this range to find its equivalent in mm. Negative values represent lengths measured in the opposite direction, useful for certain technical fields.
| Inches | Millimeters (mm) | Inches | Millimeters (mm) |
|---|---|---|---|
| -24.0 | -609.6 | 1.0 | 25.4 |
| -20.0 | -508.0 | 2.0 | 50.8 |
| -16.0 | -406.4 | 3.0 | 76.2 |
| -12.0 | -304.8 | 4.0 | 101.6 |
| -8.0 | -203.2 | 5.0 | 127.0 |
| -4.0 | -101.6 | 6.0 | 152.4 |
| -2.0 | -50.8 | 7.0 | 177.8 |
| -1.0 | -25.4 | 8.0 | 203.2 |
| 0.0 | 0.0 | 9.0 | 228.6 |
| 0.5 | 12.7 | 10.0 | 254.0 |
| 0.75 | 19.05 | 15.0 | 381.0 |
| 12.0 | 304.8 | 20.0 | 508.0 |
| 13.0 | 330.2 | 25.0 | 635.0 |
| 14.0 | 355.6 | 26.0 | 660.4 |
Related Conversion Questions
- What’s 1 inch in millimeters exactly?
- How many mm are in one inch?
- Is 1 inch equal to 25 mm or 25.4 mm?
- How do I convert 1 inch to mm manually?
- Can I use 25.4 to convert 1 inch to mm?
- What’s the formula to change inches to millimeters for 1 inch?
- Why is 1 inch equal to 25.4 mm and not 25?
Conversion Definitions
Inch: An inch is a unit of length in the imperial and United States customary systems, equal to 1/12 of a foot or 1/36 of a yard. It is used mainly in the U.S. and UK for measuring smaller lengths, with 1 inch precisely equal to 25.4 millimeters.
Millimeter (mm): A millimeter is a metric unit of length equal to one thousandth of a meter (0.001 m). It is widely used in science, engineering, and everyday measurements around the world for precise small distances and dimensions.
Conversion FAQs
Why is one inch defined as 25.4 millimeters?
The inch has been internationally standardized to 25.4 millimeters since 1959, based on an agreement between countries using the imperial and metric systems. This exact value replaced earlier approximations to unify measurements in science and trade, ensuring consistent conversions worldwide.
Can I convert fractional inches to millimeters directly?
Yes, fractional inches can be converted by first expressing the fraction as a decimal. Then multiply by 25.4 to get millimeters. For example, ¾ inch equals 0.75, so 0.75 × 25.4 = 19.05 mm.
Are millimeters more accurate than inches for measurements?
Millimeters provide smaller units, making them better suited for precision in many applications. While inches can be subdivided into fractions, millimeters offer a decimal-based system that is easier for calculations and finer measurements.
Is the conversion factor always exactly 25.4?
Yes, the conversion factor of 25.4 mm per inch is exact by international agreement. This fixed value avoids rounding errors and helps maintain consistent measurements in manufacturing and science.
How does temperature affect inch to millimeter conversion?
Temperature can cause materials to expand or contract, affecting physical length. But the conversion factor itself remains constant since it is a defined unit ratio. Measurement accuracy depends on environmental conditions, not the conversion formula.
