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Inches to Millimeters (in to mm)
Convert inches to millimeters: 1 in = 25.4 mm. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.
Formula
1 in = 25.4 mm
millimeters = inches × 25.4 — reverse: inches = millimeters × 0.03937007874
The factor is derived from the SI definitions of both units (base unit: m) as listed in NIST SP 811; results on this page are shown to 6 significant figures, the API returns up to 12.
Worked examples
- 5 in = 127 mm
- 12.5 in = 317.5 mm
- 100 in = 2540 mm
Inches to millimeters conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 6 | 152.4 |
| 7 | 177.8 |
| 8 | 203.2 |
| 9 | 228.6 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 30 | 762 |
| 40 | 1016 |
| 50 | 1270 |
| 75 | 1905 |
| 100 | 2540 |
| 200 | 5080 |
| 250 | 6350 |
| 500 | 12700 |
| 1000 | 25400 |
FAQ
How many millimeters are in one inch?
1 in = 25.4 mm. The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.
What is the formula to convert inches to millimeters?
Multiply the value in inches by 25.4: millimeters = inches × 25.4. For example, 5 in = 127 mm.
How do I convert millimeters back to inches?
Multiply by the inverse factor 0.03937007874 (inches = millimeters × 0.03937007874), or use the millimeters-to-inches page.
Related conversions
Machine access
- API:
GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=in&to_unit=mm - MCP: server
https://tttkmbb.com/mcp, toolconvert_unitswith{"value":5,"from_unit":"in","to_unit":"mm"} - Markdown: https://tttkmbb.com/conversion/inches-to-mm.md · JSON: https://tttkmbb.com/conversion/inches-to-mm.json (add
?value=for a result) · Units: /api/v1/units?quantity=length - OpenAPI operationId:
convert_units. Freshness:static. Authentication: none.