Disclosure: This post contains affiliate links, which means we may earn a commission if you purchase through our links at no extra cost to you.
1 inch equals 25.4 millimeters.
The conversion from inches to millimeters is done by multiplying the inch value by 25.4, because one inch is exactly defined as 25.4 millimeters in the international system. This means for every inch measurement, the equivalent in millimeters can be found by this multiplication.
Table of Contents
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is:
millimeters = inches × 25.4
Since one inch is exactly 25.4 millimeters, multiplying the number of inches by 25.4 gives the length in millimeters. The formula works because millimeter is a smaller unit, so it takes more millimeters to equal one inch.
For example, if you have 3 inches:
- Multiply 3 by 25.4
- 3 × 25.4 = 76.2 millimeters
- So, 3 inches equals 76.2 mm
Conversion Example
- 2.5 inches:
- Multiply 2.5 by 25.4
- 2.5 × 25.4 = 63.5 mm
- Therefore, 2.5 inches is 63.5 mm
- 0.75 inches:
- Multiply 0.75 by 25.4
- 0.75 × 25.4 = 19.05 mm
- So, 0.75 inches equals 19.05 mm
- 10 inches:
- Multiply 10 by 25.4
- 10 × 25.4 = 254 mm
- Hence, 10 inches is 254 mm
- 5.2 inches:
- Multiply 5.2 by 25.4
- 5.2 × 25.4 = 132.08 mm
- Means 5.2 inches equal 132.08 mm
- 15 inches:
- Multiply 15 by 25.4
- 15 × 25.4 = 381 mm
- Therefore, 15 inches converts to 381 mm
Conversion Chart
The chart below shows inches from -24.0 to 26.0 converted into millimeters. You can look up any value to get its millimeter equivalent by multiplying the inch number by 25.4.
| Inches | Millimeters (mm) | Inches | Millimeters (mm) |
|---|---|---|---|
| -24.0 | -609.6 | 1.0 | 25.4 |
| -20.0 | -508.0 | 5.0 | 127.0 |
| -16.0 | -406.4 | 10.0 | 254.0 |
| -12.0 | -304.8 | 15.0 | 381.0 |
| -8.0 | -203.2 | 20.0 | 508.0 |
| -4.0 | -101.6 | 25.0 | 635.0 |
| 0.0 | 0.0 | 26.0 | 660.4 |
Use the chart by finding the inch value you need in the left or right column, then see the corresponding millimeter value next to it. Negative values show lengths below zero, useful for calculations involving offsets or directions.
Related Conversion Questions
- How many millimeters are in 1 inch exactly?
- What is the formula to convert 1 inch to mm?
- Why does 1 inch equal 25.4 millimeters?
- Can I convert 1 inch to mm without a calculator?
- Is 1 inch the same in all countries when converting to mm?
- How precise is the conversion from 1 inch to millimeters?
- What tools can I use to convert 1 inch to mm quickly?
Conversion Definitions
Inch: An inch is a unit of length commonly used in the United States and other countries, equal to 1/12 of a foot. It is used to measure small distances and objects, precisely defined as exactly 25.4 millimeters since 1959 by international agreement.
Millimeter (mm): A millimeter is a metric unit of length equal to one thousandth of a meter. It is widely used in science, engineering, and everyday measurements for small distances. One millimeter is exactly 0.03937 inches.
Conversion FAQs
Is the 1 inch to mm conversion exact or approximate?
The conversion of 1 inch to 25.4 millimeters is exact, defined by international agreement since 1959. It’s not an approximation, which means that every inch measurement corresponds to exactly 25.4 millimeters without rounding errors.
Why is the inch defined as 25.4 millimeters?
The inch was standardized to 25.4 millimeters to unify measurement systems between countries using imperial and metric units. This definition allows precise and consistent conversions globally, removing variations that existed before this standardization.
Can I use this conversion for very small or very large measurements?
Yes, the same conversion factor applies regardless of the size of the measurement. Whether you measure fractions of an inch or many inches, multiplying by 25.4 gives the correct millimeter equivalent, although very small measurements might need higher decimal precision.
How do rounding errors affect inch to mm conversions?
Rounding errors can occur if you limit decimal places in the result, but since 25.4 is exact, the main source of error is input precision. Using more decimals improves accuracy, but for everyday use, rounding to two or three decimals is sufficient.
Are there any tools recommended for converting inches to millimeters?
Besides manual calculations, online converters and calculator apps help convert inches to millimeters quickly. The conversion tool provided here uses JavaScript for instant results, useful for quick estimations without external devices.
