When designers and manufacturing companies specify surface finishes more often than not we’re talking in micrometres (µm), but what exactly is a µm?

1 µm is 0.001mm or one thousandth of one millimetre.  In other words it is a very fine measurement and as such it can be hard to comprehend.  So the best way to understand it for many of us is to compare it to everyday things we’d know, such as a cigarette paper, human hair, paperclip wire or needle.

This image from our partners Haas illustrates how these items measure up and what a µm equates to in comparison.   For more details on their range of machining centres please visit their website at: http://www.haas-schleifmaschinen.de/en/

In comparison to microinches (written as µin or µ”) 1 µm = approximately 40 µ”.  1 µ” being equal to one millionth of an inch (0.000001”).  (So a 15µm surface finish = 600µ” and a 320µ” surface finish = 8µm as examples of conversions).

To understand more about surface reading types and how they are calculated, please see our post on A Guide to Understanding Surface Roughness Measurement Types

Post written by
Stephen Lewis-Brammer
General Manager