1 inch equals 25.4 millimeters.
To convert inches to millimeters, you multiply the number of inches by 25.4, because one inch is defined as exactly 25.4 millimeters. This conversion is precise and widely used in engineering and manufacturing.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches (in) to millimeters (mm) is:
millimeters = inches × 25.4
This works because the international agreement defines 1 inch as exactly 25.4 millimeters. So, when converting, you multiply the length in inches by 25.4 to get the length in millimeters.
For example, converting 1 inch to millimeters:
- Start with 1 inch
- Multiply by 25.4: 1 × 25.4
- The result is 25.4 mm
Conversion Example
- Convert 3 inches to millimeters:
- 3 × 25.4 = 76.2 mm
- Multiply the inches by 25.4 to get millimeters
- Convert 0.5 inches to millimeters:
- 0.5 × 25.4 = 12.7 mm
- Half an inch equals twelve point seven millimeters
- Convert 10 inches to millimeters:
- 10 × 25.4 = 254 mm
- Ten inches is two hundred fifty-four millimeters
- Convert 0.125 inches to millimeters:
- 0.125 × 25.4 = 3.175 mm
- One eighth of an inch equals three point one seven five millimeters
- Convert 7.25 inches to millimeters:
- 7.25 × 25.4 = 184.15 mm
- Multiply seven point two five by 25.4 to get millimeters
Conversion Chart
This chart shows inches values from -24.0 to 26.0 and their equivalent in millimeters. You can read across a row to find an inch value and its corresponding millimeters, helping quick reference without calculation.
| Inches (in) | Millimeters (mm) |
|---|---|
| -24.0 | -609.6 |
| -20.0 | -508.0 |
| -16.0 | -406.4 |
| -12.0 | -304.8 |
| -8.0 | -203.2 |
| -4.0 | -101.6 |
| 0.0 | 0.0 |
| 4.0 | 101.6 |
| 8.0 | 203.2 |
| 12.0 | 304.8 |
| 16.0 | 406.4 |
| 20.0 | 508.0 |
| 24.0 | 609.6 |
| 26.0 | 660.4 |
Related Conversion Questions
- How many millimeters are in 1 inch exactly?
- What is the formula to convert 1 inch to millimeters?
- Can 1 inch be converted to millimeters without rounding?
- Why is 1 inch equal to 25.4 millimeters?
- Is there a quick way to change inches to millimeters for 1 inch?
- How precise is the conversion from 1 inch to millimeters?
- What tools can I use to convert 1 inch into millimeters?
Conversion Definitions
in: The inch (in) is a unit of length mainly used in the United States, Canada, and the United Kingdom. It equals exactly 25.4 millimeters by international agreement. Inches are used in many fields such as construction, manufacturing, and engineering for measuring small distances and objects.
mm: The millimeter (mm) is a metric unit of length equal to one thousandth of a meter. It is commonly used worldwide for precise measurements in science, engineering, and manufacturing. Millimeters provide a fine scale for measurement, often preferred for small dimensions or technical drawings.
Conversion FAQs
Is the conversion factor from inches to millimeters ever changed?
No, the factor 25.4 is fixed and internationally accepted. Since 1959, the inch has been defined as exactly 25.4 millimeters to standardize measurements globally. This avoids confusion and maintains consistency.
Why does the conversion multiply inches by 25.4, not any other number?
The value 25.4 comes from an international agreement defining the inch length in metric units. Because the metric system is based on meters, and 1 inch equals exactly 25.4 millimeters, multiplication by this number converts inches into millimeters correctly.
Can I convert fractional inches directly to millimeters?
Yes, fractional inches first should be converted into decimal form, then multiplied by 25.4. For example, 1/2 inch equals 0.5 inches, so 0.5 × 25.4 equals 12.7 millimeters.
Are there rounding errors in converting inches to millimeters?
Since 1 inch is exactly 25.4 mm, no rounding error occurs in the base conversion. However, when converting decimal or fractional inch values, rounding can happen depending on decimal places used.
Is it better to convert inches to millimeters or the other way for precision?
For very small measurements, millimeters may offer better precision because they use a smaller unit. Inches are suitable for larger scales. Conversion does not affect precision if done with enough decimal places.