1 inch equals exactly 25.4 millimeters.
The inch is converted to millimeters by multiplying the inch value by 25.4 since one inch is defined as 25.4 millimeters. This conversion is exact because the international agreement set this precise value.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is:
millimeters = inches × 25.4
Since 1 inch is exactly 25.4 millimeters, multiply the inches value by 25.4 to get millimeters. This works because the inch is standardized against the metric system at that value. For example, to convert 3 inches:
- 3 inches × 25.4 = 76.2 millimeters
This simple multiplication converts any inch value to millimeters accurately.
Conversion Example
- 2.5 inches to mm:
- Multiply 2.5 by 25.4
- 2.5 × 25.4 = 63.5 mm
- So, 2.5 inches equals 63.5 millimeters
- 0.75 inches to mm:
- 0.75 × 25.4 = 19.05 mm
- Therefore, 0.75 inches is 19.05 millimeters
- 10 inches to mm:
- 10 multiplied by 25.4 equals 254 mm
- Hence, 10 inches is 254 millimeters
- 5.25 inches to mm:
- 5.25 × 25.4 = 133.35 mm
- So 5.25 inches converts to 133.35 millimeters
- 12 inches to mm:
- 12 × 25.4 = 304.8 mm
- Thus, 12 inches equals 304.8 millimeters
Conversion Chart
| Inches | 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 |
| 2.0 | 50.8 |
| 6.0 | 152.4 |
| 10.0 | 254.0 |
| 14.0 | 355.6 |
| 18.0 | 457.2 |
| 22.0 | 558.8 |
| 26.0 | 660.4 |
The chart shows inches values in the first column and their corresponding millimeters in the second. To find a conversion, locate the inch value and read across to see its millimeter equivalent. Negative values indicate lengths in the opposite direction.
Related Conversion Questions
- How many millimeters are in 1 inch exactly?
- What is the precise millimeter value for 1 inch?
- How to convert 1 inch measurement into millimeters?
- Is 1 inch equal to 25 mm or 25.4 mm?
- What’s the formula to turn 1 inch into mm?
- How many mm does 1 inch make when converted?
- Why does 1 inch equal 25.4 mm, not a round number?
Conversion Definitions
Inches: An inch is a unit of length in the imperial and US customary systems, equal to 1/12 of a foot or 1/36 of a yard. It is widely used in the United States and the United Kingdom for measuring short distances or sizes of objects. The inch has been standardized as exactly 25.4 millimeters since 1959.
Millimeters (mm): The millimeter is a metric unit of length equal to one thousandth of a meter. It is used globally for precise measurements in science, engineering, and everyday life. Millimeters allow for fine resolution in length measurement, making them useful for small objects and technical drawings.
Conversion FAQs
Why is one inch exactly 25.4 millimeters?
The inch was internationally standardized as exactly 25.4 millimeters in 1959 through an agreement among English-speaking countries. Before that, the inch varied slightly by region. This fixed value allows consistent conversions between imperial and metric lengths everywhere.
Can the conversion from inches to millimeters ever change?
The current conversion factor of 25.4 mm per inch is fixed by international treaty and won’t change. This ensures measurement consistency around the world. Changes would cause confusion in manufacturing, engineering, and commerce.
How accurate is the conversion factor 25.4?
The factor 25.4 is exact by definition, not an approximation. Since the inch is defined as exactly 25.4 millimeters, calculations using this factor are precise, with no rounding error introduced by the conversion itself.
Is there a quick way to estimate millimeters from inches without a calculator?
You can approximate by multiplying inches by 25, then adding about 10% more. For example, 4 inches × 25 = 100, plus 10% (10) equals roughly 110 mm, near the exact 101.6 mm. This is faster but less precise than using 25.4.
Why use millimeters instead of inches in measurements?
Millimeters are part of the metric system, which is decimal-based and easier for calculations, especially scientific or engineering work. Inches are used mainly in the US and UK for everyday measurements. Millimeters give finer resolution for small dimensions.