1.25 inches is equal to 31.75 millimeters.
The conversion from inches to millimeters is done by multiplying the inch value by 25.4, because one inch equals exactly 25.4 millimeters in the metric system. Therefore, 1.25 inches times 25.4 gives the equivalent length in millimeters.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches (in) to millimeters (mm) is:
mm = in × 25.4
This works because 1 inch has been internationally defined as 25.4 millimeters exactly. So multiplying any inch value by 25.4 converts it into millimeters. The factor 25.4 comes from measurement agreements and standards.
For example, to convert 1.25 inches to millimeters:
- Start with 1.25 in.
- Multiply by 25.4: 1.25 × 25.4 = 31.75
- Result: 31.75 mm
Conversion Example
- Convert 3.5 in to mm:
- Multiply 3.5 by 25.4
- 3.5 × 25.4 = 88.9 mm
- So, 3.5 inches equals 88.9 millimeters.
- Convert 0.75 in to mm:
- Multiply 0.75 by 25.4
- 0.75 × 25.4 = 19.05 mm
- Therefore, 0.75 inches equals 19.05 millimeters.
- Convert 10 in to mm:
- Multiply 10 by 25.4
- 10 × 25.4 = 254 mm
- This means 10 inches equals 254 millimeters.
- Convert 5.25 in to mm:
- Multiply 5.25 by 25.4
- 5.25 × 25.4 = 133.35 mm
- So 5.25 inches equals 133.35 millimeters.
Conversion Chart
| Inches (in) | Millimeters (mm) |
|---|---|
| -23.8 | -604.52 |
| -20.0 | -508.00 |
| -15.5 | -393.70 |
| -10.3 | -261.62 |
| -5.0 | -127.00 |
| -1.2 | -30.48 |
| 0.0 | 0.00 |
| 2.5 | 63.50 |
| 7.7 | 195.58 |
| 12.4 | 314.96 |
| 18.0 | 457.20 |
| 21.3 | 540.02 |
| 26.2 | 665.48 |
The chart shows inch values in the left column and their equivalent millimeters in the right. To use, find the inch number closest to your value then read across for the millimeter conversion. Negative values indicate lengths below zero in inches, converted similarly.
Related Conversion Questions
- How many millimeters are in 1.25 inches exactly?
- What is the formula to change 1.25 inches into millimeters?
- How to convert 1.25 in to mm without a calculator?
- Is 1.25 inches longer than 30 millimeters?
- Can I quickly find the mm value for 1.25 in using a conversion chart?
- What’s the difference between 1.25 inches and its equivalent in millimeters?
- Does 1.25 in equal 31.75 mm or a rounded number?
Conversion Definitions
in (inch): An inch is a unit of length in the imperial measurement system, equal to exactly 2.54 centimeters or 25.4 millimeters. It is commonly used in the United States, Canada, and the UK for measuring smaller distances, like the size of objects or screen dimensions.
mm (millimeter): A millimeter is a metric system unit of length equal to one thousandth of a meter. It’s frequently used to measure small lengths or thicknesses in engineering, manufacturing, and everyday applications internationally. One millimeter equals 0.03937 inches.
Conversion FAQs
Why is the inch defined as exactly 25.4 millimeters?
The inch was internationally standardized to exactly 25.4 millimeters in 1959 by agreement among English-speaking countries. Before, different countries had slightly different inch lengths. This uniform value ensures consistency in manufacturing, science, and engineering worldwide.
Can I convert inches to millimeters by just multiplying by 25?
Multiplying by 25 gives a rough estimate, but it’s not exact. The correct multiplier is 25.4. Using 25 will produce errors, especially over larger measurements, so using 25.4 is recommended for precise conversions.
Are there any tools available to convert inches to millimeters automatically?
Yes, many online converters and calculators exist, including the JavaScript tool above, which instantly converts inch values to millimeters when you input a number. This reduces human error and saves time compared to manual calculations.
Can negative inch values be converted to millimeters?
Yes, negative lengths in inches represent measurements below zero or in the opposite direction on a scale. The conversion formula applies the same way, yielding negative millimeter values corresponding to the input.
Is the conversion factor 25.4 an approximation or exact number?
The factor 25.4 is exact by international agreement. It’s not an approximation but a defined constant for converting inches to millimeters, ensuring consistent measurements globally across industries.