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I export my CAD models, which I create on Creo 2.0 (originally called Wildfire 5.0) as STL files, and import them into blender.

But when I compare their sizes, the objects shown in blender are usually bigger than the objects shown on my CAD program by approximately a factor 10.

Did blender confuses the unit? Because when I exported the object as an STL file, it didn't give me an option to set the unit. Is there a default unit for STL files?

The units I usually work with on Creo 2.0 are mm.

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Blender's default unit system is None, so it uses its own "Blender Units" (BU). But if you switch it to Metric in the Scene tab (Properties Editor), you'll notice that nothing changed. And 1 BU will now be 1m.

With Metric enabled, there will be a property available called scene Scale. You can set it to 0.1 to correct the scaling problem (granted, it's really 1:10). But I worry not all exporters will respect it.

So it might be better so Select All objects (A) and scale everything down (S, type 0.1, Enter). Make sure the scaling center is the scene origin (0,0,0), e.g. reset the 3D Cursor (N-sidebar, right-click on one of the 3 value fields and click Reset All to Default Values, or press ShiftC) and use it as Pivot Point (press .).

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Thank you, I did reconsider the scaling option, but I just want to know why it converts mm (it's original unit) to m when it is imported into blender as a STL file –  fRank87 Jan 31 at 22:19
    
Seems like there is no unit system specified in STL, but either or both, Credo and Blender may do some conversion or make assumptions about the scaling. The factor 1:10 is weird though, maybe 1 unit = 1mm in Credo export, but Blender imports 1 unit as 1cm (1:10)? "4) Generally STL file has no UNITS attached to it so its always good practice to send overall part sizes along with your STL file" (source) –  CoDEmanX Jan 31 at 22:23

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