# units of vtkNIFTIheader.GetPixDim()
**URL:** https://discourse.vtk.org/t/units-of-vtkniftiheader-getpixdim/2929
**Category:** Support
**Created:** [March 31, 2020, 7:47pm UTC](https://discourse.vtk.org/t/units-of-vtkniftiheader-getpixdim/2929 "2020-03-31T19:47:29Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@msmerps](https://discourse.vtk.org/u/msmerps)
#### Post date: [March 31, 2020, 7:47pm UTC](https://discourse.vtk.org/t/units-of-vtkniftiheader-getpixdim/2929/1 "2020-03-31T19:47:29Z")
Hi all,
I am using vtkNIFTIheader.GetPixDim() to get the spacing of NIFTI files. Can I assume that values it returns are in units of millimeters?
thank you in advance,
-Merps
---
### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [April 1, 2020, 4:23pm UTC](https://discourse.vtk.org/t/units-of-vtkniftiheader-getpixdim/2929/2 "2020-04-01T16:23:15Z")
The NIFTI units are almost always millimeters. However, if you need to be really sure, you can check the value returned by `GetXYZTUnits()`. It returns values described by [UnitsXYZTEnum](https://vtk.org/doc/nightly/html/classvtkNIFTIImageHeader.html#a0d63df721b5dda332a76ee6c102dc045), using bitfields, e.g.
```python
if (header.GetXYZTUnits() & vtkNIFTIImageHeader.UnitsSpace) == vtkNIFTIImageHeader.UnitsMM):
# units are definitely millimeters
elif (header.GetXYZTUnits() & vtkNIFTIImageHeader.UnitsSpace) == vtkNIFTIImageHeader.UnitsUnknown):
# units not defined, but we can assume they are millimeters?
else:
# units are not millimeters
```
---
### Author:  [@msmerps](https://discourse.vtk.org/u/msmerps)
#### Post date: [April 2, 2020, 2:32am UTC](https://discourse.vtk.org/t/units-of-vtkniftiheader-getpixdim/2929/3 "2020-04-02T02:32:12Z")
Thank you for yet more help, @dgobbi. That does the trick!