Micrometers to Millimeters Converter (µm ⇄ mm)

Convert micrometers to millimeters and back with a single, precise tool. Ideal for engineering drawings, machining tolerances, microscopy and any work at sub-millimeter scale.

Key fact: 1 millimeter (mm) = 1000 micrometers (µm). This converter also shows the equivalent length in meters, nanometers and inches.

Main converter – micrometers ⇄ millimeters

Bidirectional: type in either µm or mm

1 µm = 0.001 mm. Enter very small dimensions here (surface roughness, thin films, etc.).

1 mm = 1000 µm. Common in mechanical drawings and tolerances.

Presets (µm):

Extended view – nm, m and inches

Read-only: follows the µm/mm input above

These fields update automatically based on the main converter. They are useful to cross-check designs that mix metric and imperial units or microscope scales.

1 µm = 1000 nm.

1 mm = 0.001 m.

1 in = 25.4 mm (exact).

Micrometers to millimeters quick reference

The table below lists common values you often see in engineering drawings, optical components and machining tolerances.

Micrometers (µm) Millimeters (mm)
1 µm 0.001 mm
5 µm 0.005 mm
10 µm 0.01 mm
50 µm 0.05 mm
100 µm 0.1 mm
500 µm 0.5 mm
1000 µm 1 mm

How micrometers and millimeters relate

The metric system is based on powers of ten. The prefixes micro- and milli- specify how many powers of ten separate a unit from the base meter (m):

  • 1 micrometer (µm) = 10−6 meters
  • 1 millimeter (mm) = 10−3 meters

This means that 1 mm is 1000 times larger than 1 µm:

Core relationships

\(1~\text{mm} = 1000~\mu\text{m}\)

\(1~\mu\text{m} = 0.001~\text{mm}\)

Formulas

Millimeters from micrometers: \(\text{mm} = \dfrac{\mu\text{m}}{1000}\)

Micrometers from millimeters: \(\mu\text{m} = \text{mm} \times 1000\)

Worked example: 250 µm to mm

  1. Start from the formula \(\text{mm} = \dfrac{\mu\text{m}}{1000}\).
  2. Insert the value: \(\text{mm} = \dfrac{250}{1000} = 0.25~\text{mm}\).
  3. Typing 250 in the µm field of the calculator will show 0.25 mm.

Worked example: 0.02 mm to µm

  1. Use the inverse formula \(\mu\text{m} = \text{mm} \times 1000\).
  2. Insert the value: \(\mu\text{m} = 0.02 \times 1000 = 20~\mu\text{m}\).
  3. Typing 0.02 in the mm field will show 20 µm in the corresponding box.

FAQ: micrometers to millimeters

Where are micrometers used in practice?

Micrometers are common wherever dimensions are much smaller than 1 mm: surface roughness parameters, optical coatings, integrated circuits, biological cell sizes, precision machining and fine tolerance fits.

Is the conversion between µm and mm exact?

Yes. The relation 1 mm = 1000 µm is defined by the metric system and is exact. Any difference you see in different tools comes only from rounding rules in the user interface.

How does this compare to nanometers?

One micrometer is 1000 nanometers (1 µm = 1000 nm). So if you know a thickness in nanometers, you can reach millimeters in two steps: nm → µm → mm. The extended view in this calculator performs this automatically.

Why does the calculator also show inches?

Many engineers work in mixed environments where drawings or component data sheets are in imperial units while measurement data is in metric. Showing inches alongside µm and mm helps avoid mistakes when translating between these systems.