Elara Bennett1 inch is equal to 25.4 millimetres.
The conversion from inch to millimetres is based on the exact definition that one inch equals 25.4 millimetres. This fixed ratio allows us to convert any length in inches to millimetres by multiplying the inch value by 25.4.
Conversion Tool
Result in millimetres:
Conversion Formula
The formula to convert inches to millimetres is:
millimetres = inches × 25.4
This formula works because 1 inch is defined as exactly 25.4 millimetres, so multiplying the inch value by 25.4 converts it to millimetres.
Example calculation:
- Given length in inches: 2.5 inches
- Multiply by 25.4: 2.5 × 25.4 = 63.5
- Result: 2.5 inches equals 63.5 millimetres
Conversion Example
- 3 inches to millimetres:
- Multiply 3 by 25.4
- 3 × 25.4 = 76.2
- So, 3 inches equal 76.2 millimetres
- 0.75 inches to millimetres:
- 0.75 × 25.4 = 19.05
- Thus, 0.75 inches is 19.05 millimetres
- 5.2 inches to millimetres:
- Multiply 5.2 by 25.4
- 5.2 × 25.4 = 132.08
- Therefore, 5.2 inches converts to 132.08 millimetres
Conversion Chart
The chart below shows inch values from -24.0 to 26.0 and their corresponding millimetre values. Negative values indicate lengths in the opposite direction or below zero. Use this chart to quickly find approximate conversions without calculation.
| Inches | Millimetres | Inches | Millimetres |
|---|---|---|---|
| -24.0 | -609.6 | 1.0 | 25.4 |
| -22.0 | -558.8 | 3.0 | 76.2 |
| -20.0 | -508.0 | 5.0 | 127.0 |
| -18.0 | -457.2 | 7.0 | 177.8 |
| -16.0 | -406.4 | 9.0 | 228.6 |
| -14.0 | -355.6 | 11.0 | 279.4 |
| -12.0 | -304.8 | 13.0 | 330.2 |
| -10.0 | -254.0 | 15.0 | 381.0 |
| -8.0 | -203.2 | 17.0 | 431.8 |
| -6.0 | -152.4 | 19.0 | 482.6 |
| -4.0 | -101.6 | 21.0 | 533.4 |
| -2.0 | -50.8 | 23.0 | 584.2 |
| 0.0 | 0.0 | 25.0 | 635.0 |
| 2.0 | 50.8 | 26.0 | 660.4 |
| 4.0 | 101.6 | ||
| 6.0 | 152.4 | ||
| 8.0 | 203.2 | ||
| 10.0 | 254.0 | ||
| 12.0 | 304.8 | ||
| 14.0 | 355.6 | ||
| 16.0 | 406.4 | ||
| 18.0 | 457.2 | ||
| 20.0 | 508.0 | ||
| 22.0 | 558.8 | ||
| 24.0 | 609.6 |
Related Conversion Questions
- How many millimetres equals 1 inch exactly?
- What is 1 inch in millimetres with decimals?
- Is 1 inch bigger or smaller than 25 millimetres?
- How do I convert 1 inch to millimetres without a calculator?
- Why does 1 inch equal 25.4 millimetres and not 25?
- Can 1 inch be converted to millimetres in fractions?
- What is the formula to convert 1 inch into millimetres?
Conversion Definitions
Inch: An inch is a unit of length in the imperial and US customary systems, equal to exactly 2.54 centimetres or 25.4 millimetres. It is commonly used in the United States, Canada, and the UK for measuring short distances, such as screens, paper sizes, and small objects.
Millimetres: Millimetres are metric units of length, equal to one thousandth of a metre (0.001 m). It is part of the International System of Units (SI) and widely used worldwide for precise measurements in engineering, manufacturing, and science. Millimetres offer fine resolution for small distances.
Conversion FAQs
Why is one inch defined as 25.4 millimetres?
The inch was standardized internationally in 1959 when several countries agreed to define it as exactly 25.4 millimetres. This agreement removes variations from earlier definitions based on metal bars or physical rulers, ensuring consistency across measurements worldwide.
Can I convert inches to millimetres by dividing instead of multiplying?
No, converting inches to millimetres requires multiplying by 25.4 because millimetres are smaller units. Dividing would give incorrect results, as it would make the value smaller instead of larger, which contradicts the fact that 1 inch is longer than 1 millimetre.
Are inches and millimetres interchangeable in technical drawings?
Inches and millimetres are not interchangeable without conversion. Technical drawings must specify units clearly because 1 inch is 25.4 times longer than 1 millimetre. Using the wrong unit can lead to errors in manufacturing or construction, so conversion must be applied carefully.
What tools can convert inches to millimetres quickly?
Many online converters, calculator functions, and even spreadsheet software can convert inches to millimetres instantly. Physical rulers often have both scales, but for precise values, digital tools or the multiplication formula (inches × 25.4) are preferred.
Is the conversion factor always exactly 25.4?
Yes, the conversion factor is exactly 25.4 by international agreement. This exact value eliminates rounding errors and provides a universal standard for converting inches to millimetres in science, engineering, and daily use.
