12 inches is equal to 304.8 millimeters.
The conversion from inches to millimeters involves multiplying the length value in inches by 25.4, since one inch equals exactly 25.4 millimeters. So, 12 inches times 25.4 gives 304.8 mm.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inches to millimeters is:
millimeters = inches × 25.4
This works because one inch is defined as exactly 25.4 millimeters. Multiplying the number of inches by 25.4 converts the length to millimeters. For example, if you have 12 inches:
- 12 inches × 25.4 = 304.8 millimeters
The multiplication factor (25.4) acts as a scaling value to exchange inches for millimeters, since the two units measure length but in different sizes.
Conversion Example
- Convert 5 inches to mm:
- Multiply 5 by 25.4
- 5 × 25.4 = 127 mm
- So, 5 inches equals 127 millimeters.
- Convert 8.25 inches to mm:
- Multiply 8.25 by 25.4
- 8.25 × 25.4 = 209.55 mm
- Result: 209.55 millimeters.
- Convert 0.5 inches to mm:
- Multiply 0.5 by 25.4
- 0.5 × 25.4 = 12.7 mm
- Hence, 0.5 inches equals 12.7 millimeters.
- Convert 20 inches to mm:
- Multiply 20 by 25.4
- 20 × 25.4 = 508 mm
- Therefore, 20 inches equal 508 millimeters.
Conversion Chart
The chart below shows values from -13.0 to 37.0 inches converted to millimeters. Find the inch value you’re interested in, then read across to see the corresponding millimeter measurement.
| Inches | Millimeters (mm) |
|---|---|
| -13.0 | -330.2 |
| -10.0 | -254.0 |
| -5.0 | -127.0 |
| 0.0 | 0.0 |
| 5.0 | 127.0 |
| 10.0 | 254.0 |
| 12.0 | 304.8 |
| 15.0 | 381.0 |
| 20.0 | 508.0 |
| 25.0 | 635.0 |
| 30.0 | 762.0 |
| 37.0 | 939.8 |
Related Conversion Questions
- How many millimeters are in 12 inches exactly?
- What is the formula to convert 12 inches to millimeters?
- Is 12 inches longer than 300 mm?
- Can I convert 12 inches to mm without a calculator?
- How to quickly convert 12 inches into millimeters?
- Why does 12 inches equal 304.8 mm?
- What tools can help me convert 12 inches to mm online?
Conversion Definitions
Inches: An inch is a unit of length in the imperial system, equal to 1/12 of a foot. It is used primarily in the United States, Canada, and the United Kingdom for measuring small distances or objects. One inch equals exactly 2.54 centimeters or 25.4 millimeters.
Millimeters: A millimeter is a metric unit of length, one thousandth of a meter. It is widely used worldwide for precise measurements in science, engineering, and everyday tasks. One millimeter equals 0.03937 inches, making it much smaller than an inch.
Conversion FAQs
Why is the conversion factor between inches and millimeters exactly 25.4?
The value 25.4 mm per inch was agreed internationally in 1959 to standardize measurements. Previously, different countries used slightly different definitions. This exact number ensures consistency in manufacturing, engineering, and science worldwide.
Can I convert inches to millimeters by rough estimation without a calculator?
You can estimate by knowing 1 inch is about 25 mm. Multiply inches by 25 for a close estimate. For example, 12 inches × 25 = 300 mm, which is close to the exact 304.8 mm. This method works for quick mental calculations but has some error.
What happens if I convert negative inches to millimeters?
Negative values represent lengths in the opposite direction or below a reference point. Converting negative inches to millimeters uses the same formula, multiplying by 25.4, but the result is negative. For example, -5 inches equals -127 mm.
Are inches and millimeters interchangeable in technical drawings?
While both measure length, inches and millimeters are not directly interchangeable without conversion. Technical drawings specify units to avoid confusion. Using the wrong unit without converting can cause errors in measurements, manufacturing, or construction.
Does the conversion change if measuring thickness or width?
No, the conversion factor from inches to millimeters remains the same regardless of the dimension being measured. Whether length, width, or thickness, multiply inches by 25.4 to get millimeters.
Last Updated : 29 June, 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.