Millimeters to Micrometers
Type a value in either box to convert between millimeters and micrometers. The factor is 1000.
| Millimeters | Micrometers |
|---|---|
| 1 mm | 1000 µm |
| 2 mm | 2000 µm |
| 3 mm | 3000 µm |
| 5 mm | 5000 µm |
| 10 mm | 10000 µm |
| 25 mm | 25000 µm |
| 50 mm | 50000 µm |
| 100 mm | 100000 µm |
How to use
- Enter a value in the Millimeters field.
- The Micrometers figure appears immediately — no button to press.
- Typing in the Micrometers field converts back to Millimeters the same way.
- Use the reference table for the values that come up most often.
Millimeters to Micrometers formula
The factor from millimeters to micrometers is 1000.
µm = mm × 1000
Put another way, one millimeter is exactly 1,000 micrometers.
Why this factor: the millimeter and the micrometer are both defined against the meter, so dividing one definition by the other gives 1000 directly. Both definitions are set out in full below.
To go the other way, divide by 1000 — or use the Micrometers to Millimeters converter, which is the same calculation reversed.
Worked example
Start with 12 mm. Multiply by 1000 to get 12000 µm.
12 mm × 1000 = 12000 µm
The converter above does this for any value you type, in either direction.
What is a millimeter?
A millimeter is one thousandth of a meter — the working precision unit of manufacturing and construction.
Definition: Exactly 0.001 meter by SI prefix definition.
Where it is used: Engineering drawings, machining tolerances, timber and steel dimensions, rainfall totals.
What is a micrometer?
A micrometer, or micron, is one millionth of a meter — the scale of cells, fibers and semiconductor features.
Definition: Exactly 1×10⁻⁶ meter by SI prefix definition. Symbol µm.
Where it is used: Filtration ratings, particulate sizes (PM2.5 is 2.5 µm), fiber diameters, optical wavelengths.
Worth knowing: Often written 'micron' in industry. A human hair is roughly 70 µm across.
Millimeters vs Micrometers
The millimeter and the micrometer belong to the same family of units, so converting between them is usually a matter of shifting a decimal point or applying a small whole-number factor.
Frequently asked questions
How many micrometers are in a millimeter?
One millimeter equals 1000 micrometers.
What is the formula to convert millimeters to micrometers?
Multiply the number of millimeters by 1000. To reverse it, divide by 1000 instead.
How do I convert micrometers back to millimeters?
Divide by 1000, which is the same as multiplying by 0.001.
How many micrometers are in 10 millimeters?
10 mm works out to 10000 µm.
Is there anything to watch out for with micrometers?
Often written 'micron' in industry. A human hair is roughly 70 µm across.
How is the millimeter defined?
Exactly 0.001 meter by SI prefix definition.