# Units in VTK
**URL:** https://discourse.vtk.org/t/units-in-vtk/12892
**Category:** Support
**Created:** [December 13, 2023, 7:46am UTC](https://discourse.vtk.org/t/units-in-vtk/12892 "2023-12-13T07:46:43Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Mordrago](https://discourse.vtk.org/u/Mordrago)
#### Post date: [December 13, 2023, 7:46am UTC](https://discourse.vtk.org/t/units-in-vtk/12892/1 "2023-12-13T07:46:43Z")
Hello!
What units of measurement does vtk use? I have scans from a CMM with an accuracy of 5 micrometers. I would like to display them by adding the primitives I created to them. Here the question arises what units does vtk accept? The stl file does not contain such information, so as I understand it I have to make sure that these units are specified at the outset?
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### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [December 13, 2023, 8:12am UTC](https://discourse.vtk.org/t/units-in-vtk/12892/2 "2023-12-13T08:12:57Z")
There is no units in VTK, only numbers.
If your numbers are in micrometers, then your unit is micrometers.
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### Author:  [@Mordrago](https://discourse.vtk.org/u/Mordrago)
#### Post date: [December 13, 2023, 9:43am UTC](https://discourse.vtk.org/t/units-in-vtk/12892/3 "2023-12-13T09:43:16Z")
Ok thanks, so i should define units at start
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### Author:  [@1116](https://discourse.vtk.org/u/1116)
#### Post date: [May 10, 2024, 6:54pm UTC](https://discourse.vtk.org/t/units-in-vtk/12892/4 "2024-05-10T18:54:06Z")
Hi, Mathieu, I’m wondering how that number maps to the pixels. For example, when I set space of the grid as 1, what does this 1 represent, how does vtk know how many pixel it should use for this space, thanks! Is it just a relative value?
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### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [May 14, 2024, 6:25am UTC](https://discourse.vtk.org/t/units-in-vtk/12892/5 "2024-05-14T06:25:43Z")
That depends on the camera parameters and the projection to the screenspace.