Millimeters to Inches Converter
Convert millimeters to inches precisely. Essential for hardware and tools.
Common Conversions
Related Calculators
What is Millimeters to Inches Converter?
The millimeters to inches converter translates small metric measurements to imperial inches. One inch equals exactly 25.4 millimeters, making the conversion straightforward: divide mm by 25.4 to get inches. Millimeter-to-inch conversion is essential in hardware, manufacturing, and precision engineering, where metric and imperial tools and components must be compared or substituted for each other.
Millimeters are the standard unit for small-scale precision measurements in the metric world: screw and bolt diameters, drill bit sizes, wall thickness, gap measurements, and mechanical tolerances. In the US, the same measurements are expressed in fractions of an inch. Workers, hobbyists, and engineers regularly need to convert between these systems when sourcing parts, reading specifications, or communicating with suppliers across measurement system boundaries.
How to Use This Calculator
Enter the value in millimeters and the converter instantly displays the equivalent in inches (decimal). Formula: inches = mm ÷ 25.4. For fractional inch results, note that common fractions are: 1/16 = 0.0625 in, 1/8 = 0.125 in, 3/16 = 0.1875 in, 1/4 = 0.25 in, 5/16 = 0.3125 in, 3/8 = 0.375 in, 7/16 = 0.4375 in, 1/2 = 0.5 in.
Worked Examples
Bolt Size Conversion
An M8 metric bolt has an 8 mm diameter. Converting: 8 ÷ 25.4 = 0.315 inches. The closest imperial bolt is 5/16 inch (0.3125 inches) but they are not interchangeable. An M10 bolt (10 mm = 0.394 in) is close to but not equivalent to 3/8 inch (0.375 in).
Drill Bit Sizes
A 6 mm drill bit: 6 ÷ 25.4 = 0.236 inches ≈ 15/64 inch (0.234 in). A 12 mm bit: 12 ÷ 25.4 = 0.472 in ≈ 15/32 inch. Choosing the nearest fractional inch bit is common practice when metric bits are unavailable.
Smartphone Camera Sensor
Camera sensor sizes are often listed in mm. A 1/1.7-inch sensor (the fraction of an inch name is historical, not a direct inch measurement) equates to approximately 7.53 × 5.64 mm sensor area. Understanding mm dimensions helps compare actual sensor sizes across different brands and models.
Millimeters to Inches Conversion Table
| Millimeters | Decimal Inches | Fractional Inches (approx) |
|---|---|---|
| 1 mm | 0.0394 in | 1/25" |
| 2 mm | 0.0787 in | 5/64" |
| 3 mm | 0.1181 in | 1/8" |
| 4 mm | 0.1575 in | 5/32" |
| 5 mm | 0.1969 in | 13/64" |
| 6 mm | 0.2362 in | 15/64" |
| 7 mm | 0.2756 in | 9/32" |
| 8 mm | 0.3150 in | 5/16" |
| 9 mm | 0.3543 in | 23/64" |
| 10 mm | 0.3937 in | 25/64" |
| 12 mm | 0.4724 in | 15/32" |
| 15 mm | 0.5906 in | 19/32" |
| 16 mm | 0.6299 in | 5/8" |
| 20 mm | 0.7874 in | 25/32" |
| 25 mm | 0.9843 in | 63/64" |
| 30 mm | 1.1811 in | 1 3/16" |
| 50 mm | 1.9685 in | 1 31/32" |
| 100 mm | 3.9370 in | 3 15/16" |
Benefits of Using This Calculator
- Identify imperial inch equivalents for metric bolts, screws, and fasteners
- Convert drill bit sizes between metric (mm) and imperial (fractional inch) systems
- Translate pipe and tube outer diameters between measurement systems
- Find compatible imperial hardware when metric parts are unavailable
- Read and interpret metric technical drawings when working with imperial tools
- Compare product specifications from different regional suppliers
Practical Tips
- Remember: 25.4 mm = 1 inch exactly. So 25 mm ≈ 1 inch (98.4% of an inch).
- Common metric-to-fractional benchmarks: 3 mm ≈ 1/8", 6 mm ≈ 1/4", 13 mm ≈ 1/2", 19 mm ≈ 3/4", 25 mm ≈ 1".
- Metric and imperial fasteners are NOT interchangeable even when similar in size — always use the correct specification.
- For precision work, always use decimal inches rather than fractions to avoid accumulated rounding errors.
Key Takeaways
- 11 mm = 0.03937 inches; divide mm by 25.4 to convert to inches.
- 225 mm ≈ 1 inch (within 1.6%); exactly 25.4 mm = 1 inch.
- 310 mm ≈ 3/8 inch; 6 mm ≈ 1/4 inch — useful hardware size benchmarks.
- 4Metric and imperial hardware sizes are similar but not interchangeable.
Frequently Asked Questions
To convert millimeters to inches, divide by 25.4 (since 1 inch = exactly 25.4 mm). The formula is: inches = mm ÷ 25.4. For example, 50 mm ÷ 25.4 = 1.969 inches, and 100 mm ÷ 25.4 = 3.937 inches. You can also multiply by 0.03937 for the same result.
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