# MassProperties
**URL:** https://discourse.vtk.org/t/massproperties/2753
**Category:** Support
**Created:** [March 4, 2020, 6:31pm UTC](https://discourse.vtk.org/t/massproperties/2753 "2020-03-04T18:31:50Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@ShaneKirkbride](https://discourse.vtk.org/u/ShaneKirkbride)
#### Post date: [March 4, 2020, 6:31pm UTC](https://discourse.vtk.org/t/massproperties/2753/1 "2020-03-04T18:31:50Z")
I’m looking at the vtkMassProperties class. How is the mass computed with no knowledge of the pixel or slice spacing of the PolyData?
---
### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [March 4, 2020, 8:31pm UTC](https://discourse.vtk.org/t/massproperties/2753/2 "2020-03-04T20:31:50Z")
Points of a polydata are not defined on a rectilinear grid, so there are no pixels or slices. Instead, point coordinates are floating-point values, defined directly in the world coordinate system.
If you create polydata from image (e.g., using marching cubes) then the conversion algorithm takes into account pixel and slice spacing.
---
### Author:  [@ShaneKirkbride](https://discourse.vtk.org/u/ShaneKirkbride)
#### Post date: [March 4, 2020, 8:36pm UTC](https://discourse.vtk.org/t/massproperties/2753/3 "2020-03-04T20:36:58Z")
@lassoan so if my units are mm in my image and I’m looking at this example:
[https://lorensen.github.io/VTKExamples/site/Cxx/Utilities/MassProperties/](https://lorensen.github.io/VTKExamples/site/Cxx/Utilities/MassProperties/)
What units would the volume output be in? L or mL? or mm^3?
Thanks,
~Shane
---
### Author:  [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [March 4, 2020, 8:54pm UTC](https://discourse.vtk.org/t/massproperties/2753/4 "2020-03-04T20:54:37Z")
Volume = length \* length \* length, so if your length unit is mm then volume unit is mm \* mm \* mm.