1 inch equals 25.4 millimeters.
The inch (in) is a unit of length in the imperial system, and millimeter (mm) is a metric unit. Converting 1 inch to millimeters involves multiplying by the exact conversion factor of 25.4, because 1 inch is defined as exactly 25.4 millimeters.
Conversion Tool
Result in mm:
Conversion Formula
The conversion from inches to millimeters uses the formula:
Millimeters (mm) = Inches (in) × 25.4
This formula works because the inch was internationally agreed to be exactly 25.4 millimeters. Multiplying the length in inches by 25.4 scales it to the metric system.
Example calculation:
- Given: 1 in
- Multiply: 1 × 25.4 = 25.4 mm
Therefore, 1 inch equals 25.4 millimeters.
Conversion Example
- 3.5 inches to millimeters:
- Multiply 3.5 by 25.4
- 3.5 × 25.4 = 88.9 mm
- The result is 88.9 millimeters
- 0.75 inches to millimeters:
- Calculate 0.75 × 25.4
- 0.75 × 25.4 = 19.05 mm
- So, 0.75 inches equals 19.05 millimeters
- 10 inches to millimeters:
- Multiply 10 by 25.4
- 10 × 25.4 = 254 mm
- Thus, 10 inches converts to 254 millimeters
- 5.25 inches to millimeters:
- Calculate 5.25 × 25.4
- 5.25 × 25.4 = 133.35 mm
- Result: 133.35 millimeters
Conversion Chart
| Inches (in) | 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 |
| 26.0 | 660.4 |
To use the chart, find the inch value on the left column and see its equivalent millimeters on the right. Negative values represent lengths below zero, useful for measuring offsets or directions in some contexts.
Related Conversion Questions
- How many millimeters are in 1 inch exactly?
- What is the formula to convert 1 inch to millimeters?
- Is 1 inch equal to 25 or 26 millimeters?
- How do I convert 1 inch to mm without a calculator?
- Why is 1 inch defined as 25.4 millimeters?
- What is the difference between 1 inch and 1 millimeter?
- Can 1 inch be converted to millimeters using multiplication?
Conversion Definitions
In (inch): Inch is an imperial unit of length equal to 1/12 of a foot or 1/36 of a yard. It is commonly used in the United States and the UK for measuring small distances, lengths, and heights. The inch is defined as exactly 25.4 millimeters by international agreement.
Mm (millimeter): Millimeter is a metric unit of length equal to one thousandth of a meter. It is used worldwide in science, engineering, and everyday measurements to express very small distances. The millimeter provides a precise scale for measuring things smaller than a centimeter.
Conversion FAQs
Why is 1 inch exactly 25.4 millimeters?
The inch was standardized internationally in 1959 by an agreement among English-speaking countries. Before that, the inch varied slightly between countries. The value 25.4 mm was chosen for simplicity and to align the imperial system with the metric system without changing existing measurements.
Can I convert inches to millimeters without a calculator?
Yes, by knowing the conversion factor 25.4, you can multiply mentally or estimate. For example, 1 inch is about 25 mm, so 2 inches is roughly 50 mm, and so on. For more exact results, a calculator helps but rough conversions work for many practical purposes.
Is the conversion factor 25.4 always accurate?
Yes, because 1 inch is defined exactly as 25.4 millimeters by international standards, so the factor never changes. This exact definition ensures consistency worldwide across all measurements involving inches and millimeters.
Are there other units related to inches and millimeters?
Yes, inches relate to feet and yards in the imperial system, where 12 inches equals 1 foot. Millimeters relate to centimeters and meters in the metric system, where 10 mm equals 1 cm and 1000 mm equals 1 meter. These unit families help scale measurements up or down.
What kind of tools use inch to millimeter conversions?
Many engineering, manufacturing, and design tools use this conversion to switch between imperial and metric units. Rulers, calipers, CAD software, and machining equipment often convert dimensions from inches to millimeters for precision and compatibility.