inches to mm Converter
length converter
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Hardware, tooling, and engineering drawing dimensions.
Converted value
25.4mm
Calculated from your value and units at 6-decimal precision.
Common pairs
Examples: 1, 1/2, 5 3/8, 12.5
Live conversionExact basis: 1 in = 25.4 mm by definition. Commas and scientific notation are supported (for example 1,234.5 or 1e-3).
Conversion updates automatically as you change value, units, or precision.
Advanced options
Batch conversion
Convert multiple values only when you need them, without crowding the main workflow.
Examples
Conversion details
Formula and exact relation
- 1 in = 25.4 mm
- 1 mm = 0.03937007874 in
Formula form: mm = in × 25.4. Display rounding follows your selected precision and does not change base conversion math.
Context outputs
Normalized inches
1 in
1/16-inch increment
1"
Quick table (in → mm)
| in | mm |
|---|---|
| 0.125 | 3.175 |
| 0.25 | 6.35 |
| 0.5 | 12.7 |
| 0.75 | 19.05 |
| 1 | 25.4 |
| 1.5 | 38.1 |
| 2 | 50.8 |
Common hardware sizes (inch → mm)
| Inch size | Millimeters |
|---|---|
| 1/8" | 3.175 mm |
| 3/16" | 4.762 mm |
| 1/4" | 6.35 mm |
| 5/16" | 7.938 mm |
| 3/8" | 9.525 mm |
| 1/2" | 12.7 mm |
| 5/8" | 15.875 mm |
| 3/4" | 19.05 mm |
| 7/8" | 22.225 mm |
| 1" | 25.4 mm |
Formula
millimeters = inches × 25.4 - One inch equals 25.4 millimeters by definition.
- Multiply inch value by 25.4.
- Result is reported in millimeters.
Example
Worked example: 2.5 in to mm
- 1 2.5 × 25.4 = 63.5
- 2 Unit = millimeters
- 3 Precision can be adjusted as needed
2.5 inches equals 63.5 mm.
How
- Enter inch value as a decimal or fraction.
- Keep conversion direction as in to mm.
- Review live output in millimeters and copy when needed.
Avoid
- Dividing by 25.4 instead of multiplying in this direction.
- Mixing inch fractions and decimals without conversion.
- Ignoring unit labels in mixed metric/imperial documents.
Table
| Conversion | Result |
|---|---|
| 1 in to mm | 25.4 mm |
| 1/4 in to mm | 6.35 mm |
| 1/2 in to mm | 12.7 mm |
| 1 3/8 in to mm | 34.925 mm |
| 2 in to mm | 50.8 mm |
| 5 in to mm | 127 mm |
FAQ
Is 25.4 exact or approximate?
It is exact by international definition of the inch.
Can I use this for screw and drill sizes?
Yes, it is useful for converting imperial hardware dimensions to metric equivalents.
Does this tool support fractions and mixed inches?
Yes. You can enter 1/4, 1 3/8, 12.5, and values with inch suffixes such as 1 3/8 in, then copy the millimeter result or full report details.
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