Millimeters to Micrometers Converter
Enter a length in millimeters and the converter gives the same length in micrometers, also called microns. The guide covers the factor of 1,000, worked examples and a table of common values.
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Created by the Reeliy Editorial Team. Last updated: Oct 19, 2026
How many micrometers are in a millimeter?
One millimeter equals exactly 1,000 micrometers. The micrometer, symbol μm, is one millionth of a meter (10-6 m), while the millimeter is one thousandth (10-3 m), so the ratio between them is 1,000. The micrometer is often called a micron, an older name that is still common in manufacturing and filtration.
1 mm = 1,000 μm 1 μm = 0.001 mmExact: both prefixes are defined as powers of ten.
Millimeters versus micrometers
A millimeter is a unit you can see and feel: it is the finest mark on a ruler. A micrometer is a thousand times smaller and sits below the limit of the naked eye. Typical office paper is about 0.1 mm (100 μm) thick, a human hair is roughly 50 to 100 μm wide, and a red blood cell is about 7 to 8 μm across.
Micrometers are the working unit for coating and film thickness, surface roughness, filter pore size, machining tolerances and microscopy. Datasheets frequently mix the two units, for instance a sheet quoted in millimeters with a tolerance in microns, so converting quickly avoids slips of three orders of magnitude.
How to convert mm to μm
micrometers = millimeters × 1,000
- Type the size in millimeters into the first field.
- Read the micrometers from the second field; it recalculates on each change.
- By hand, multiply by 1,000, which moves the decimal point three places to the right.
Worked examples
Copper foil. A standard 1 oz printed-circuit copper layer is about 0.035 mm thick. 0.035 × 1,000 = 35 μm.
Sheet material. A 0.8 mm plastic sheet is 0.8 × 1,000 = 800 μm thick.
A fine tolerance. A shaft must be within ±0.0025 mm of its nominal size. That is 0.0025 × 1,000 = 2.5 μm.
Back to millimeters. A 70 μm hair is 70 ÷ 1,000 = 0.07 mm. The micrometers to millimeters converter does that direction for you.
Millimeters to micrometers conversion table
| Millimeters (mm) | Micrometers (μm) |
|---|---|
| 0.001 | 1 |
| 0.01 | 10 |
| 0.05 | 50 |
| 0.1 | 100 |
| 0.5 | 500 |
| 1 | 1,000 |
| 2.5 | 2,500 |
| 5 | 5,000 |
| 10 | 10,000 |
| 25 | 25,000 |
| 100 | 100,000 |
Precision and nearby converters
The answer is rounded to four decimal places and shown without thousands separators, so 123456789.123456 mm appears as 123456789123.456 μm. Multiplying by 1,000 is exact in principle, so any difference you see from a hand calculation comes only from that rounding.
Going smaller, one millimeter is also 1,000,000 nanometers; use the millimeters to nanometers converter. For larger steps there are millimeters to centimeters and millimeters to inches, and the rest of the family lives under dimension converters.
Frequently asked questions
How many micrometers are in a millimeter?
There are exactly 1,000 micrometers in one millimeter.
How do I convert mm to microns?
Multiply the millimeters by 1,000. For example, 0.25 mm is 250 microns.
Is a micron the same as a micrometer?
Yes. Micron is an older name for the micrometer (μm), one millionth of a meter. The two terms mean the same length.
Which is larger, a millimeter or a micrometer?
The millimeter is larger by a factor of 1,000. A micrometer is 0.001 mm.
References
Cite this converter and page
If you use this page in your work, you can cite it as:
Reeliy Editorial Team. (2026). Millimeters to Micrometers Converter. Reeliy. https://reeliy.com/converters/convert-mm-to-micrometer“Millimeters to Micrometers Converter.” Reeliy, 2026, https://reeliy.com/converters/convert-mm-to-micrometer.