4 inch equals 101.6 millimeters.
To convert inches to millimeters, you multiply the number of inches by 25.4, because one inch is exactly 25.4 millimeters. So, 4 inches times 25.4 equals 101.6 mm.
Conversion Tool
Result in mm:
Conversion Formula
The formula to convert inch to millimeter is:
Millimeters = Inches × 25.4
Because 1 inch equals exactly 25.4 millimeters, you multiply inches by 25.4 to get millimeters. This works due the international agreement on inch definition, which fixed the inch as exactly 25.4 mm.
Example calculation for 4 inches:
- Start with 4 inches.
- Multiply 4 by 25.4.
- 4 × 25.4 = 101.6 mm.
Conversion Example
- Convert 7 inches to millimeters:
- 7 × 25.4 = 177.8 mm.
- The multiplication converts inches to mm by scaling.
- Convert 0.5 inch to millimeters:
- 0.5 × 25.4 = 12.7 mm.
- Half an inch equals 12.7 millimeters.
- Convert 12.25 inches to millimeters:
- 12.25 × 25.4 = 311.15 mm.
- Multiply the decimal inches by 25.4 for precise mm.
Conversion Chart
| Inches | Millimeters (mm) |
|---|---|
| -21.0 | -533.4 |
| -20.0 | -508.0 |
| -10.0 | -254.0 |
| -5.0 | -127.0 |
| 0.0 | 0.0 |
| 1.0 | 25.4 |
| 5.0 | 127.0 |
| 10.0 | 254.0 |
| 15.0 | 381.0 |
| 20.0 | 508.0 |
| 25.0 | 635.0 |
| 29.0 | 736.6 |
The chart shows inch values in left column and their equivalent millimeters in right. You can find the inch you want, then read across to see its mm value. This helps quick conversion without calculation.
Related Conversion Questions
- How many millimeters are 4 inches exactly?
- What is the formula to convert 4 inch to mm?
- Is 4 inches equal to 100 mm or 101.6 mm?
- How do I convert 4 inches to millimeters manually?
- What is the difference between 3.9 and 4 inch in mm?
- Can I use 25.4 to convert 4 inches into mm?
- Why does 4 inch convert to 101.6 mm instead of 100 mm?
Conversion Definitions
Inch: An inch is a unit of length in the imperial and US customary systems, equal to exactly 25.4 millimeters. It is commonly used in the United States for measuring small distances and objects like screens, paper sizes, or hardware. It originated from the width of a thumb.
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 manufacturing. A millimeter is one ten-thousandth of a kilometer, making it ideal for small-scale lengths.
Conversion FAQs
Why is one inch equal to exactly 25.4 millimeters?
The inch was standardized as exactly 25.4 millimeters by international agreement in 1959 between English-speaking countries. Before that, inch definitions varied slightly. This fixed value ensures uniformity in measurements worldwide, especially for trade and manufacturing.
Can the conversion from inch to mm cause rounding errors?
Since the inch to millimeter conversion uses a fixed exact factor, rounding errors can happen only when decimal places are limited. Using more decimal places reduces error. For everyday use, rounding to 2-4 decimal places is accurate enough.
Is the conversion factor the same for all types of inches?
Yes, the international inch is standardized to 25.4 mm. However, in the past, different countries used slightly different inch lengths, like the US survey inch. Those are obsolete now but may cause confusion in historical data.
How do I convert fractional inches to millimeters?
First, convert the fraction to a decimal (e.g., 3/4 inch = 0.75 inch), then multiply by 25.4. For example, 3/4 inch × 25.4 = 19.05 mm. This method works for any fraction of an inch.
Why use millimeters instead of inches in measurements?
Millimeters belong to the metric system, which is decimal-based and easier for calculations and conversions. Many industries prefer mm for precision and international standards, while inches remain common in the US and UK.