Inch to Millimeter Converter
Use this free calculator to quickly convert inches (in) to millimeters (mm). Enter any number, including decimals.
What this conversion inch to mm calculator does
This calculator converts imperial length values in inches to metric values in millimeters. It is useful for manufacturing, woodworking, engineering drawings, 3D printing, home improvement, and international product measurements where precision matters.
Instead of doing mental math each time, you can type the inch value once and get an instant, accurate result. The tool supports both whole numbers and decimal values.
Inch to mm formula
The number 25.4 is exact by definition. That means every inch is exactly 25.4 millimeters. If your project requires tight tolerances, this fixed conversion factor gives you reliable results.
Quick examples
- 1 inch = 25.4 mm
- 2 inches = 50.8 mm
- 0.5 inch = 12.7 mm
- 12 inches = 304.8 mm
Common inch to millimeter conversion chart
| Inches | Millimeters |
|---|---|
| 1/16 in (0.0625) | 1.5875 mm |
| 1/8 in (0.125) | 3.175 mm |
| 1/4 in (0.25) | 6.35 mm |
| 3/8 in (0.375) | 9.525 mm |
| 1/2 in (0.5) | 12.7 mm |
| 3/4 in (0.75) | 19.05 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 6 in | 152.4 mm |
| 12 in | 304.8 mm |
Where this conversion is commonly used
1) Engineering and technical drawings
Many parts are designed in one unit system but manufactured in another. Converting inches to mm correctly helps avoid dimensional mismatch, assembly issues, and costly rework.
2) DIY and home projects
Tools, bolts, and materials can come labeled in imperial or metric units depending on brand and region. A quick inch-to-mm conversion helps you choose the right drill bit, fastener, or replacement part.
3) 3D printing and CNC work
CAD files and slicers often use millimeters by default. If your reference dimension is in inches, convert it accurately before generating toolpaths or print settings.
Tips for accurate measurement conversion
- Use decimal inches if possible for cleaner calculations.
- Keep at least 3 decimal places in mm for precision work.
- Only round at the final step to avoid accumulated error.
- Double-check critical dimensions before cutting or machining.
Frequently asked questions
Is 25.4 rounded?
No. The value 25.4 mm per inch is exact.
Can I enter negative values?
Yes. The calculator accepts negative numbers, which can be useful in coordinate systems or directional offsets.
Does this tool convert mm to inches too?
This page is focused on inch to mm conversion. For reverse conversion, divide mm by 25.4.
Final note
If you regularly move between imperial and metric measurements, bookmarking this conversion inch to mm calculator can save time and prevent mistakes. Just enter inches, click convert, and get instant millimeter results.