# Micrometers to Millimeters (μm to mm)

> Convert micrometers to millimeters: 1 μm = 0.001 mm. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `micrometers-to-mm` · Quantity: Length (`length`, base unit m) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/micrometers-to-mm · This document: https://tttkmbb.com/conversion/micrometers-to-mm.md · JSON: https://tttkmbb.com/conversion/micrometers-to-mm.json (add `?value=` for a result)

## Formula

- `1 μm = 0.001 mm`
- `millimeters = micrometers × 0.001`
- Reverse: `micrometers = millimeters × 1000`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 μm = 0.005 mm
- 12.5 μm = 0.0125 mm
- 100 μm = 0.1 mm

## Conversion table

| Micrometers (μm) | Millimeters (mm) |
| --- | --- |
| 1 | 0.001 |
| 2 | 0.002 |
| 3 | 0.003 |
| 4 | 0.004 |
| 5 | 0.005 |
| 6 | 0.006 |
| 7 | 0.007 |
| 8 | 0.008 |
| 9 | 0.009 |
| 10 | 0.01 |
| 15 | 0.015 |
| 20 | 0.02 |
| 25 | 0.025 |
| 30 | 0.03 |
| 40 | 0.04 |
| 50 | 0.05 |
| 75 | 0.075 |
| 100 | 0.1 |
| 200 | 0.2 |
| 250 | 0.25 |
| 500 | 0.5 |
| 1000 | 1 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=um&to_unit=mm` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"um","to_unit":"mm"}`
- All length units: https://tttkmbb.com/api/v1/units?quantity=length · full converter: [Length Converter](https://tttkmbb.com/conversion/length.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many millimeters are in one micrometer?**

1 μm = 0.001 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 micrometers to millimeters?**

Multiply the value in micrometers by 0.001: millimeters = micrometers × 0.001. For example, 5 μm = 0.005 mm.

**How do I convert millimeters back to micrometers?**

Multiply by the inverse factor 1000 (micrometers = millimeters × 1000), or use the millimeters-to-micrometers page.

## Related conversions

- [Millimeters to micrometers](https://tttkmbb.com/conversion/mm-to-micrometers.md) (reverse)
- [Kilometers to Miles](https://tttkmbb.com/conversion/km-to-miles.md)
- [Miles to Kilometers](https://tttkmbb.com/conversion/miles-to-km.md)
- [Meters to Feet](https://tttkmbb.com/conversion/meters-to-feet.md)
- [Feet to Meters](https://tttkmbb.com/conversion/feet-to-meters.md)
- [Centimeters to Inches](https://tttkmbb.com/conversion/cm-to-inches.md)
- [Inches to Centimeters](https://tttkmbb.com/conversion/inches-to-cm.md)
- [Millimeters to Inches](https://tttkmbb.com/conversion/mm-to-inches.md)
- [Inches to Millimeters](https://tttkmbb.com/conversion/inches-to-mm.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)