Why Convert Inches to Millimeters?
Converting between inches (in) and millimeters (mm) is one of the most common length conversions. Whether for engineering, cooking, travel, or science, knowing how to quickly convert in to mm saves time and prevents errors.
Length conversions between in and mm 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 Inches to Millimeters
To convert inches to millimeters, use the following formula:
mm = in × 25.4
Example: 1 in = 25.4 mm
For example, 5 in = 127 mm, 10 in = 254 mm, and 100 in = 2540 mm. Our calculator above performs this conversion instantly with full precision — no rounding errors.
Common Use Cases
- Half-inch pipe diameter (plumbing): 0.5 in = 12.7 mm
- Quarter-inch audio jack: 0.25 in = 6.35 mm
- 6-inch smartphone screen diagonal: 6 in = 152.4 mm
- One-inch sensor (camera): 1 in = 25.4 mm
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 in to mm, 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 mm" is clear.
Pro Tips
- Memorize the factor: 1 in = 25.4 mm. For quick mental math, remember this base conversion.
- Quick reference: 5 in = 127 mm · 10 in = 254 mm · 25 in = 635 mm · 50 in = 1270 mm · 100 in = 2540 mm
- Bookmark this page: Save this converter for instant access. It works offline once loaded — no internet needed.
Inches to Millimeters Conversion Table
| in | mm |
|---|---|
| 0.01 in | 0.254 mm |
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
| 500 in | 12700 mm |
| 1000 in | 25400 mm |
All values in this table are mathematically exact per NIST SP 811.