1.25 inches equals 31.75 millimeters.
This conversion is based on the fact that one inch equals exactly 25.4 millimeters, so multiplying 1.25 by 25.4 gives you the length in millimeters. This process allows you to translate measurements from the imperial system to the metric system efficiently.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is simple: multiply the number of inches by 25.4. This number 25.4 is the fixed length of one inch in millimeters, established by international agreement.
Why this works: because the inch and millimeter are both units of length, but from different measurement systems. To convert from inches to millimeters, you multiply by 25.4, which scales the imperial length into metric length.
Example calculation:
- Start with 1.25 inches.
- Multiply 1.25 × 25.4 = 31.75.
- Result is 31.75 millimeters.
Conversion Example
- Convert 3 inches to mm:
- Multiply 3 × 25.4 = 76.2 mm.
- This means 3 inches corresponds to 76.2 millimeters.
- Convert 0.5 inches to mm:
- Calculate 0.5 × 25.4 = 12.7 mm.
- Half an inch equals 12.7 millimeters.
- Convert 7.8 inches to mm:
- Multiply 7.8 × 25.4 = 198.12 mm.
- So 7.8 inches converts to 198.12 millimeters.
- Convert 10 inches to mm:
- Calculate 10 × 25.4 = 254 mm.
- 10 inches is exact 254 millimeters.
- Convert 2.33 inches to mm:
- Multiply 2.33 × 25.4 = 59.182 mm.
- Rounded, that is 59.182 millimeters.
Conversion Chart
The table below shows inch values from -23.8 up to 26.2 with their equivalent in millimeters. Use the chart by finding your inch value in the left column, and then reading across to find the millimeter result.
| Inches | Millimeters (mm) |
|---|---|
| -23.8 | -604.52 |
| -20.0 | -508.00 |
| -15.5 | -393.70 |
| -10.1 | -256.54 |
| -5.75 | -146.05 |
| -1.0 | -25.40 |
| 0.0 | 0.00 |
| 1.25 | 31.75 |
| 3.5 | 88.90 |
| 7.7 | 195.58 |
| 10.0 | 254.00 |
| 14.4 | 365.76 |
| 18.9 | 480.06 |
| 22.0 | 558.80 |
| 26.2 | 665.48 |
Related Conversion Questions
- How many millimeters are in 1.25 inches exactly?
- What is 1.25 inches converted into millimeters for engineering use?
- Is 1.25 inches the same as 31.75 mm in precise measurement?
- How to convert 1.25 inch length into millimeters manually?
- What formula do I use to get mm from 1.25 inches?
- How to convert 1.25 inches to millimeters using JavaScript?
- Why does 1.25 inch equal 31.75 mm, how is this calculated?
Conversion Definitions
Inches: Inches are a unit of length in the imperial and US customary systems, defined as exactly 25.4 millimeters. It’s commonly used in the United States and UK for measuring small distances, lengths of objects, or screen sizes. One inch equals 1/12 of a foot.
Millimeters: Millimeters are units of length in the metric system, where 1000 millimeters make one meter. The millimeter is used internationally for precise measurements in science, engineering, and manufacturing. It is one thousandth of a meter, making it suitable for measuring small lengths.
Conversion FAQs
Can I convert inches to millimeters without a calculator?
Yes, by remembering that 1 inch equals 25.4 millimeters, you can multiply the inch value by 25.4 manually. For rough estimates, multiplying by 25 is close enough, but for exact results, use 25.4. This method works fine for most everyday measurements.
What happens if I convert negative inches to millimeters?
Negative inches represent lengths in the opposite direction or certain coordinate positions. When converting, multiply the negative inch value by 25.4, resulting in a negative millimeter value that preserves the direction or position in metric units.
Is 25.4 an approximate or exact number in conversions?
The value 25.4 is defined exactly by international agreement since 1959. It is not approximate, so all conversions using this number are precise, which ensures consistency in measurements across systems and devices worldwide.
Why is the conversion factor 25.4 instead of a rounded number?
The conversion uses 25.4 millimeters because it matches the inch defined in terms of the metric system with precision. Rounding could lead to errors in engineering, manufacturing, and science, so the exact number is used to keep measurements accurate.
Can fractional inches be converted easily to millimeters?
Yes, fractional inches like 1.25 or 0.5 can be converted by first converting the fraction to decimal form, then multiplying by 25.4. This method works well for any fraction or decimal inches, giving accurate millimeter results.