12 inches equals 304.8 millimeters.
The conversion from inches to millimeters is done by multiplying the inch value by 25.4. Since one inch is exactly 25.4 millimeters, 12 inches times 25.4 gives 304.8 millimeters.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is:
millimeters = inches × 25.4
This works because one inch was defined to be exactly 25.4 millimeters by international agreement. So every inch measurement can be multiplied by 25.4 to get the equivalent length in millimeters.
Example: To convert 12 inches to millimeters:
- Multiply 12 by 25.4
- 12 × 25.4 = 304.8
- Therefore, 12 inches equals 304.8 millimeters
Conversion Example
- 5 inches to mm:
- Multiply 5 × 25.4
- 5 × 25.4 = 127
- 5 inches is 127 millimeters
- 8.5 inches to mm:
- Multiply 8.5 × 25.4
- 8.5 × 25.4 = 215.9
- Result is 215.9 millimeters
- 0.25 inches to mm:
- Multiply 0.25 × 25.4
- 0.25 × 25.4 = 6.35
- So 0.25 inches equals 6.35 millimeters
- 20 inches to mm:
- Multiply 20 × 25.4
- 20 × 25.4 = 508
- 20 inches converts to 508 millimeters
Conversion Chart
The table below shows the conversion of values from -13.0 inches up to 37.0 inches to millimeters. You can find the inch value on the left column and the equivalent millimeters on the right column. Use this to quickly lookup a conversion without calculations.
| Inches | Millimeters (mm) |
|---|---|
| -13.0 | -330.2 |
| -10.0 | -254.0 |
| -7.0 | -177.8 |
| -4.0 | -101.6 |
| -1.0 | -25.4 |
| 0.0 | 0.0 |
| 1.0 | 25.4 |
| 4.0 | 101.6 |
| 7.0 | 177.8 |
| 10.0 | 254.0 |
| 13.0 | 330.2 |
| 16.0 | 406.4 |
| 19.0 | 482.6 |
| 22.0 | 558.8 |
| 25.0 | 635.0 |
| 28.0 | 711.2 |
| 31.0 | 787.4 |
| 34.0 | 863.6 |
| 37.0 | 939.8 |
Related Conversion Questions
- How many millimeters are in 12 inches exactly?
- What is 12 inch measurement in mm for engineering use?
- Can 12 inches be converted to millimeters for CAD drawings?
- Is 12 inch equal to 300 mm or more?
- How do I convert 12″ to mm without a calculator?
- What’s the millimeter value of 12 inches in construction?
- How precise is converting 12 inch to millimeters?
Conversion Definitions
Inch: An inch is a unit of length in the imperial and US customary systems, equal to 1/12 of a foot or 2.54 centimeters. It is commonly used in the United States, Canada, and the United Kingdom for measuring smaller distances, especially in manufacturing and construction.
Millimeter (mm): A millimeter is a metric unit of length equal to one-thousandth of a meter. It is used worldwide for precise measurements in science, engineering, and everyday life. Millimeters offer finer resolution than centimeters, making it useful for small dimensions.
Conversion FAQs
Why is one inch exactly 25.4 millimeters?
The inch was internationally defined as exactly 25.4 millimeters in 1959 during an agreement between countries using the imperial and metric systems. This fixed value replaced earlier approximations to make conversions consistent worldwide, especially important in trade and manufacturing.
Can fractions of an inch be converted to millimeters?
Yes, fractions of an inch can be converted by first converting the fraction to a decimal, then multiplying by 25.4. For example, 3/8 inch is 0.375 inches, and 0.375 × 25.4 gives 9.525 millimeters.
How precise is the conversion from inch to millimeters?
The conversion is exact since an inch is defined to be 25.4 millimeters exactly. However, rounding during calculations can introduce slight differences. Using more decimal places helps improve accuracy for sensitive applications.
Is the conversion different for miles or feet?
The conversion factor of 25.4 mm per inch applies only to inches. Feet and miles convert differently: 1 foot equals 304.8 mm, as it contains 12 inches, and 1 mile equals 1,609,344 mm based on feet conversion.
Why do some tools show slight differences converting inches to millimeters?
Some tools might use rounded or approximated values, or limited decimal places, causing minor differences. Using the exact value of 25.4 mm per inch ensures consistent results. Differences also appear if the input is rounded before conversion.
Last Updated : 06 July, 2025
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Sandeep Bhandari holds a Bachelor of Engineering in Computers from Thapar University (2006). He has 20 years of experience in the technology field. He has a keen interest in various technical fields, including database systems, computer networks, and programming. You can read more about him on his bio page.