Why Convert Millimeters to Inches?
Converting between millimeters (mm) and inches (in) is one of the most common length conversions. Whether for engineering, cooking, travel, or science, knowing how to quickly convert mm to in saves time and prevents errors.
Length conversions between mm and in are essential in international travel, construction, and sports. Airline carry-on luggage limits are typically defined in centimeters (55×40×20 cm), but US travelers think in inches. Architects and contractors regularly convert between metric and imperial measurements when working on international projects. In athletics, track distances may be in meters while road races use miles or kilometers.
How to Convert Millimeters to Inches
To convert millimeters to inches, use the following formula:
in = mm × 0.03937007874
Example: 1 mm = 0.03937007874 in
For example, 5 mm = 0.1968503937 in, 10 mm = 0.3937007874 in, and 100 mm = 3.937007874 in. Our calculator above performs this conversion instantly with full precision — no rounding errors.
Common Use Cases
- iPhone 15 Pro thickness (8.25 mm): 8.3 mm = 0.3267716535 in
- Thickness of two stacked coins: 3 mm = 0.1181102362 in
- Width of a smartphone screen: 150 mm = 5.905511811 in
- Typical screw diameter (M4.5): 4.5 mm = 0.1771653543 in
Common Mistakes to Avoid
- Confusing similar units: Don't mix up meters (m) with miles (mi) — they differ by a factor of ~1600. Always check the unit symbol.
- Rounding too early: When converting mm to in, carry at least 4 decimal places in intermediate calculations to avoid compounding errors.
- Forgetting unit labels: Always write the unit symbol after the number. "5.5" is ambiguous — "5.5 in" is clear.
Pro Tips
- Memorize the factor: 1 mm = 0.03937007874 in. For quick mental math, remember this base conversion.
- Quick reference: 5 mm = 0.1968503937 in · 10 mm = 0.3937007874 in · 25 mm = 0.9842519685 in · 50 mm = 1.968503937 in · 100 mm = 3.937007874 in
- Bookmark this page: Save this converter for instant access. It works offline once loaded — no internet needed.
Millimeters to Inches Conversion Table
| mm | in |
|---|---|
| 0.01 mm | 0.0003937007874 in |
| 0.1 mm | 0.003937007874 in |
| 0.5 mm | 0.01968503937 in |
| 1 mm | 0.03937007874 in |
| 2 mm | 0.07874015748 in |
| 5 mm | 0.1968503937 in |
| 10 mm | 0.3937007874 in |
| 20 mm | 0.7874015748 in |
| 50 mm | 1.968503937 in |
| 100 mm | 3.937007874 in |
| 500 mm | 19.68503937 in |
| 1000 mm | 39.37007874 in |
All values in this table are mathematically exact per NIST SP 811.