01 inch is equal to 25.4 millimeters (mm).
The conversion from inches to millimeters is based on the exact definition that 1 inch equals 25.4 mm. So, to convert inches to millimeters, you multiply the inch value by 25.4, giving you the length in millimeters.
Conversion Tool
Result in mm:
Conversion Formula
The conversion formula for inches to millimeters is based on the fixed equivalence that 1 inch = 25.4 millimeters. This exact value is internationally accepted and used in measurements.
To convert inches (in) to millimeters (mm), multiply the inch value by 25.4:
mm = inches × 25.4
Why this works: the inch is defined as exactly 25.4 mm, so the multiplication gives the direct equivalent length in millimeters.
Example calculation:
- If you have 1 inch, then mm = 1 × 25.4 = 25.4 mm
- For 0.5 inch, mm = 0.5 × 25.4 = 12.7 mm
Conversion Example
- Convert 3 inches to mm:
- Multiply 3 by 25.4
- 3 × 25.4 = 76.2 mm
- The result is 76.2 millimeters
- Convert 5.5 inches to mm:
- Calculate 5.5 × 25.4
- 5.5 × 25.4 = 139.7 mm
- This means 5.5 inches equals 139.7 millimeters
- Convert 0.25 inch to mm:
- Multiply 0.25 by 25.4
- 0.25 × 25.4 = 6.35 mm
- So 0.25 inch is 6.35 millimeters
Conversion Chart
| Inch | Millimeters (mm) |
|---|---|
| -24.0 | -609.6 |
| -20.0 | -508.0 |
| -15.5 | -393.7 |
| -10.0 | -254.0 |
| -5.0 | -127.0 |
| -1.0 | -25.4 |
| 0.0 | 0.0 |
| 1.0 | 25.4 |
| 2.5 | 63.5 |
| 5.0 | 127.0 |
| 10.0 | 254.0 |
| 15.0 | 381.0 |
| 20.0 | 508.0 |
| 25.0 | 635.0 |
| 26.0 | 660.4 |
This chart helps you quickly find the millimeter equivalent for inch values between -24.0 and 26.0. To use, locate the inch value on left column and see the converted millimeters on the right.
Related Conversion Questions
- How many millimeters are in 1 inch exactly?
- What is the precise conversion from 1 inch to mm?
- Is 1 inch longer or shorter than 25 mm?
- How do I convert 1 inch measurement to millimeters?
- Does 1 inch equal 25.4 mm or a different number?
- What is the formula for changing 1 inch into millimeters?
- How many mm make up 1 inch length?
Conversion Definitions
Inch: An inch is a unit of length in the imperial and US customary systems, defined as exactly 25.4 millimeters. It is commonly used to measure small distances or lengths, especially in the United States, United Kingdom, and Canada. One inch equals 1/12 of a foot.
Millimeter (mm): A millimeter is a metric unit of length equal to one-thousandth of a meter. It is widely used worldwide for precise measurements in science, engineering, and everyday applications. One millimeter equals 0.03937 inches.
Conversion FAQs
Why is 1 inch exactly equal to 25.4 millimeters?
The inch was legally defined as exactly 25.4 millimeters in 1959 by international agreement among English-speaking countries. This standardization allows for consistent measurements when converting between imperial and metric units, removing previous fractional discrepancies.
Can I use the simple factor 25 to convert inches to millimeters?
Using 25 as a factor gives an approximate value but it is not precise. Since 1 inch equals 25.4 mm exactly, using 25 results in small errors, which can be important in technical or engineering contexts where accuracy matters.
What happens when I convert negative inch values to millimeters?
Negative inch values represent lengths or displacements in the opposite direction. When converting, multiply the negative inch value by 25.4, resulting in a negative millimeter value, preserving the direction or sign of the measurement.
Is the conversion factor 25.4 used for other units besides millimeters?
The 25.4 value specifically relates to converting inches to millimeters. For other units like centimeters or meters, different factors apply. For example, 1 inch equals 2.54 centimeters, which is 10 times less than 25.4 mm.
How accurate is the conversion from inches to millimeters in everyday use?
The conversion is exactly accurate as 1 inch equals 25.4 mm by definition. However, in everyday use, rounding or measuring tool precision might introduce slight inaccuracies, but the formula and factor are exact.
