# Calculation of Wall Shear Stress

**URL:** https://discourse.paraview.org/t/calculation-of-wall-shear-stress/8667
**Category:** ParaView Support
**Created:** [December 20, 2021, 7:05pm UTC](https://discourse.paraview.org/t/calculation-of-wall-shear-stress/8667 "2021-12-20T19:05:28Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![GKk](https://discourse.paraview.org/user_avatar/discourse.paraview.org/gkk/32/8235_2.png) [@GKk](https://discourse.paraview.org/u/GKk)
#### Post date: [December 20, 2021, 7:05pm UTC](https://discourse.paraview.org/t/calculation-of-wall-shear-stress/8667/1 "2021-12-20T19:05:28Z")

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Hello,

I want to calculate the Wall Shear Stress in a 3D case. Although I found this [https://www.paraview.org/pipermail/paraview/2016-October/038305.html](https://solution), I have some questions. Firstly, I followed the instructions and I finally I was not able to take the dot product of Gradient and Velocity because the Gradient was analyzed into 9 components. Secondly I cannot understand why we need the normals on the surface and not the tangentials because I want to calculate the Shear stress and not the Normal one.

Thanks