What Is a Micron?
A micron is one-millionth of a meter — the unit used for cells, particles, and precision tolerances. Here is what it means and how to convert it.
Last updated: 2026-05-21
Definition
A micron is a unit of length equal to one-millionth of a meter. Written out, that is 1 micron = 1 micrometer = 0.001 mm = 1×10−6 m ≈ 0.0000394 in. It is the standard unit for measuring objects too small to see with the naked eye — biological cells, airborne particles, thin films, and machined surface tolerances.
The word micron is the historical name. The official SI term is micrometer, with the symbol µm (the Greek letter mu followed by m). The International System of Units formally retired “micron” and its old symbol “µ” in 1967, but engineers, filtration specialists, and scientists still use the word every day. For practical purposes, micron and micrometer mean exactly the same thing.
Because a micron is one-thousandth of a millimeter, it sits between the millimeter and the nanometer on the metric scale: 1 mm = 1,000 µm, and 1 µm = 1,000 nanometers.
Micron Conversions
Microns convert cleanly into the rest of the metric system by powers of ten. The imperial equivalents involve the inch, which is defined as exactly 25,400 microns. The “mil” (also called a thou) is one-thousandth of an inch and is common in manufacturing.
| From | To | Value |
|---|---|---|
| 1 micron (µm) | millimeters | 0.001 mm |
| 1 micron (µm) | centimeters | 0.0001 cm |
| 1 micron (µm) | meters | 1×10−6 m |
| 1 micron (µm) | inches | 0.0000394 in |
| 1 micron (µm) | mils / thou | 0.0394 mil |
| 1 millimeter | microns | 1,000 µm |
| 1 inch | microns | 25,400 µm |
Everyday Examples
The micron is hard to picture because nothing at that scale is visible. The table below anchors it to familiar objects, from a strand of hair down to the structures inside a microchip.
| Object | Approximate Size |
|---|---|
| Human hair (width) | ~70 µm |
| Pollen grain | ~15–50 µm |
| Red blood cell | ~7–8 µm |
| PM2.5 air pollution particle | 2.5 µm |
| Bacteria | ~1–10 µm |
| Fine water filter rating | 1–5 µm |
| Modern semiconductor node | < 0.01 µm (a few nanometers) |
These examples explain why the micron shows up across so many fields. Air-quality standards target PM2.5 particles — 2.5 microns and smaller — because they slip deep into the lungs. Water and HVAC filters are rated in microns to state the smallest particle they trap. Medical labs measure cells in microns, and chip makers push features far below a single micron into the nanometer range.
Need to move between microns and millimeters, inches, or mils for a real measurement? Use the length converter for instant, precise results across every metric and imperial unit.