1 inch equals exactly 25.4 millimeters (mm).
The inch is converted to millimeters by multiplying the length value in inches by 25.4, because one inch is defined as 25.4 mm internationally. This conversion provides a precise way to switch between imperial and metric units.
Conversion Tool
Result in mm:
Conversion Formula
The conversion formula from inches to millimeters is:
millimeters = inches × 25.4
This works because by international agreement, one inch is exactly 25.4 millimeters long. You multiply the number of inches by 25.4 to get the length in millimeters.
Example:
If you have 1 inch and want to convert to mm:
- Multiply 1 (inch) by 25.4
- 1 × 25.4 = 25.4 mm
- So, 1 inch is 25.4 mm
Conversion Example
- 2.5 inches to mm:
- Start with 2.5 inches
- Multiply 2.5 by 25.4
- 2.5 × 25.4 = 63.5 mm
- Therefore, 2.5 inches equals 63.5 mm
- 0.75 inches to mm:
- Take 0.75 inches
- Multiply 0.75 × 25.4
- 0.75 × 25.4 = 19.05 mm
- So, 0.75 inch converts to 19.05 mm
- 10 inches to mm:
- Begin with 10 inches
- 10 × 25.4 = 254 mm
- That means 10 inches equals 254 millimeters
- 5.25 inches to mm:
- Multiply 5.25 by 25.4
- 5.25 × 25.4 = 133.35 mm
- Thus, 5.25 inches is 133.35 mm
Conversion Chart
The chart below shows inch values from -24.0 to 26.0 converted to millimeters. You can use this to find quick conversions without calculation.
| Inches | Millimeters (mm) |
|---|---|
| -24.0 | -609.6 |
| -20.0 | -508.0 |
| -15.0 | -381.0 |
| -10.0 | -254.0 |
| -5.0 | -127.0 |
| 0.0 | 0.0 |
| 5.0 | 127.0 |
| 10.0 | 254.0 |
| 15.0 | 381.0 |
| 20.0 | 508.0 |
| 25.0 | 635.0 |
| 26.0 | 660.4 |
To use the chart, find the inch value in the first column, then read its equivalent millimeters in the second column. Negative values indicate lengths measured in the opposite direction or below a reference point.
Related Conversion Questions
- How many millimeters are in 1 inch exactly?
- What is 1 inch converted to mm with decimal precision?
- Can 1 inch be expressed as a whole number in millimeters?
- Is 25.4 mm always equal to 1 inch?
- How to convert 1 inch to mm using a calculator?
- Why does 1 inch equal 25.4 millimeters?
- What’s the formula to change 1 inch into mm?
Conversion Definitions
Inches: An inch is a unit of length in the imperial system, equal to exactly 1/12 of a foot. It’s commonly used in the US, UK, and Canada for measuring small distances and objects. One inch equals 25.4 millimeters by international agreement, allowing precise metric conversion.
Millimeters (mm): A millimeter is a metric unit of length, equal to one thousandth of a meter. It is used worldwide for scientific, engineering, and everyday measurements. Millimeters measure small distances with high precision, making them ideal for technical drawings, manufacturing, and crafts.
Conversion FAQs
Why is 1 inch equal exactly to 25.4 millimeters?
The length of one inch was internationally standardized to 25.4 millimeters in 1959 by agreement between countries using the imperial and metric systems. Before this, definitions varied slightly. This fixed value ensures consistent measurement conversions worldwide.
Can I convert inches to millimeters without a calculator?
Yes, you can use the formula multiplying inches by 25.4. For quick estimates, remember 1 inch roughly equals 25 mm. For more precision, multiplying by 25.4 gives the exact result. Conversion charts also help to avoid calculations.
Does converting 1 inch to mm change with temperature or conditions?
No, the conversion is a fixed mathematical relationship. However, physical objects may expand or contract with temperature changes, but the inch to millimeter conversion factor remains constant as a unit definition.
Can I use this conversion for very small or very large measurements?
Yes, the formula applies to any magnitude of inches, including fractional and large values. For extremely small lengths, millimeters or smaller units like micrometers may be more convenient, but conversion remains correct.
How precise is the 25.4 mm conversion factor for 1 inch?
The value 25.4 mm per inch is exact by international agreement, so it’s precise for all practical and scientific purposes. Measurements will be as accurate as the tools used for measuring lengths, not the conversion factor itself.