How to make a 3D model and set the correct dimensions?

Question

3D

I need to make a case for my project, it includes parts of a certain size, for example an ultrasonic sensor and I need to make it so that the sending and receiving parts of it look out of the case, for this I need to create the correct dimensions for printing and I want to know how this indicates which process needs to go through, so that we can endow the model made in a blender or in other software with dimensions and it is desirable to indicate this in centimeters. There will be many details in the case that will have to look out in a certain way, buttons, etc., how to attribute to all this the size that the printer will create when printing?

Answer 1

In 3D printing, it is assumed that 1 model unit is 1mm . Also
, in Blender, you can set the units to metric, then all the lengths you will have are not just numbers, but 1m, 25cm, 2mm, etc.
But I did not check how it is then exported to STL, because the model is usually in simple units, counting them as millimeters.