1 inch equals 25.4 millimeters (mm).
Table of Contents
An inch is converted to millimeters by multiplying the inch value by 25.4. This number comes from the exact international agreement that defined an inch to be exactly 25.4 mm, so converting between these units is straightforward.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is: millimeters = inches × 25.4. This works because by international standard, 1 inch is exactly 25.4 millimeters.
When you multiply any value in inches by 25.4, you get the equivalent length in millimeters.
Example calculation for 1 inch:
- Start with 1 inch.
- Multiply 1 by 25.4.
- 1 × 25.4 = 25.4 mm.
Conversion Example
- 5 inches to mm:
– Take 5 inches.
– Multiply 5 × 25.4.
– Result: 127 mm.
– So, 5 inches equal 127 millimeters. - 0.75 inches to mm:
– Begin with 0.75 inches.
– Multiply 0.75 × 25.4.
– Result: 19.05 mm.
– Therefore, 0.75 inches are 19.05 millimeters. - 12.3 inches to mm:
– Start with 12.3 inches.
– Multiply 12.3 × 25.4.
– Result: 312.42 mm.
– Hence, 12.3 inches is 312.42 millimeters. - 0 inches to mm:
– Zero times any number is zero.
– So, 0 × 25.4 = 0 mm.
– Meaning zero inches equals zero millimeters. - 2.5 inches to mm:
– Multiply 2.5 by 25.4.
– Result: 63.5 mm.
– Thus, 2.5 inches correspond to 63.5 millimeters.
Conversion Chart
The chart below lists inch values from -24.0 to 26.0 and their equivalent millimeters. Use it to quickly find approximate conversions without calculation. Negative values represent lengths in the opposite direction or below a reference point.
| 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 |
| -1.0 | -25.4 |
| 0.0 | 0.0 |
| 1.0 | 25.4 |
| 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’s the difference between an inch and a millimeter for measurement?
- Can I convert 1 inch to millimeters without a calculator?
- Is 1 inch greater than 25 millimeters or less?
- How do I convert 1 inch to mm in a formula?
- Why is 1 inch equal to 25.4 mm and not some other number?
- What tools can help me convert 1 inch to millimeters quickly?
Conversion Definitions
Inches: An inch is a unit of length in the imperial system, equal to 1/12 of a foot. It is used in countries like the United States for measuring small distances and sizes, especially in construction, manufacturing, and everyday items. Exactly 1 inch equals 25.4 millimeters by international agreement.
Millimeters (mm): A millimeter is a metric unit of length equal to one thousandth of a meter. It’s used worldwide for precise measurements in engineering, science, and manufacturing. Millimeters provide a finer scale than centimeters or inches, commonly used for small dimensions and tolerances.
Conversion FAQs
Why is the inch defined as exactly 25.4 millimeters?
In 1959, an international agreement standardized the inch as exactly 25.4 millimeters to unify measurements worldwide. Before that, inches varied regionally. This exact value ensures consistency and precision across countries using imperial and metric systems.
Can negative inch values be converted to millimeters?
Yes, negative inch values represent lengths in the opposite direction or below a reference point. When converting, the negative sign is preserved, so -2 inches converts to -50.8 millimeters. The calculation process remains the same.
Is the conversion factor always 25.4?
Yes, the conversion factor from inches to millimeters is always 25.4. This is an exact, fixed value established by international standards, so no variations or approximations occur in this conversion.
How precise is the conversion when using 25.4 as a factor?
Since 25.4 is an exact number, the precision depends on how many decimal places you carry in calculations. Using more decimal points in your result increases accuracy, but 4 decimal places are usually sufficient for practical use.
Is there a simple way to estimate millimeters from inches without exact math?
A quick estimate is to multiply inches by 25, which gives a rough value slightly less than the actual millimeters. For rough work, this can be useful, but for accurate conversions, always use 25.4 as the multiplier.