Need a quick way to convert millimeters (mm) to inches (in)? You are not alone. This is one of the most common unit conversions used in home improvement, product sizing, 3D printing, engineering drawings, and online shopping.
If you want a fast calculator, this millimeter to inch conversion tool is a practical option for instant results.
What Is the mm to inches Formula?
The core formula is simple:
inches = millimeters ÷ 25.4
Why 25.4? Because exactly 25.4 millimeters equals 1 inch.
Quick Reference Conversion Chart
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 mm | 0.0394 in |
| 5 mm | 0.1969 in |
| 10 mm | 0.3937 in |
| 12 mm | 0.4724 in |
| 25 mm | 0.9843 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.9370 in |
Step-by-Step Examples
Example 1: Convert 8 mm to inches
8 ÷ 25.4 = 0.31496, so 8 mm is approximately 0.315 inches.
Example 2: Convert 30 mm to inches
30 ÷ 25.4 = 1.1811, so 30 mm is approximately 1.18 inches.
Example 3: Convert 200 mm to inches
200 ÷ 25.4 = 7.8740, so 200 mm is approximately 7.87 inches.
When Accuracy Matters Most
In some situations, rounding can lead to small but important errors. Keep more decimal places when you are working on:
- mechanical fitting and machining,
- 3D printing dimensions,
- architecture and technical drawings,
- jewelry and precision craft work.
A simple rule: for casual tasks, 2 decimals are usually enough; for technical work, use 3 to 4 decimals.
Common Mistakes to Avoid
- Multiplying by 25.4 instead of dividing (that converts inches to mm, not mm to inches).
- Rounding too early before final calculations.
- Mixing decimal inches and fractional inches without checking context.
Final Takeaway
Converting millimeters to inches is easy once you remember one number: 25.4. Divide mm by 25.4, round based on your use case, and you will get reliable results every time.