# why cleantogrid filter so slow?

**URL:** https://discourse.paraview.org/t/why-cleantogrid-filter-so-slow/17370
**Category:** ParaView Support
**Created:** [December 13, 2025, 1:27pm UTC](https://discourse.paraview.org/t/why-cleantogrid-filter-so-slow/17370 "2025-12-13T13:27:50Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![garcfd](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/g/ccd318/32.png) [@garcfd](https://discourse.paraview.org/u/garcfd)
#### Post date: [December 13, 2025, 1:27pm UTC](https://discourse.paraview.org/t/why-cleantogrid-filter-so-slow/17370/1 "2025-12-13T13:27:50Z")

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I have an octree mesh flow solution which comes from my solver ufocfd (octree)

I decided to use use “clean to grid” because it seems the only way to get gradients of density.

I noticed that the cleantogrid filter is very slow (mesh is 10million cells) and gets worse for later versions of paraview. I am using v3.98 its slow, then v5.10 is slower, and v6.0 grinds to a halt.

 ![image](https://discourse.paraview.org/uploads/default/original/3X/d/3/d3abf4fe9d4791ffa7e9407cd0aa5ea7204055a8.png)

v6.0.1 literally stops at 3%

What is going on? Is there a better way to get density gradient, instead of clean to grid?

thanks. Giles