Re: Fixing mm or inches

From: Delft Spline Systems (
Date: Tue Nov 11 2003 - 20:54:06 EET

Hi Jonathan,

STL files do not contain any information on units, nor does
the definition prescribe the units. So most software will just
assume the units to be either mm or inches, depending on the
preferences set by the user.

What happens when you change the software's Units setting
after having imported the files will depend on the application.
Our DeskProto software wil maintain the physical dimensions,
and thus change the numbers with a factor 25.4
For a different behaviour you have to first change the settings and
then import the file. As said: other applications will show
different behaviour.

For telling the part size it is sufficient to define the units,
however just to make sure it is always very wise to also mention
the actual size that the receiver can expect.

For other file formats the situation is different.
For instance IGES files contain a parameter for units settings (however
not all programs set this parameter). VRML files should be in meters
according the the format definition (however not all programs follow
this definition).

Best Regards,

Lex Lennings.

At 09:02 AM 11/11/03, you wrote:
>Is there a way to "fix" a 3D model in mm or inches?
>Also, is a "conversion" simply a matter of changing the UNITS setting in
>the software - if you have opened the model using the wrong units setting
>(say the vendor opens the model in mm instead of the original being made
>in inches) - or is it more complicated than this?
>Finally, does stl file format have some kind of unit definition?
>Occassionally a vendor asks me "how big" the model is, can I just tell
>them to open it in "inches' or "mm's"? Or do you need to communicate
>something like a X axis width or depth?
>Universal Joint: Buildings + Digital Design
>Jonathan Chertok. Principal
>Austin, Texas [512] 407 9628
>Full Service Design and Construction

Delft Spline Systems, The Netherlands.
We offer DeskProto: affordable Rapid Prototyping using CNC milling. --- website:

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