# flow rate specific area

**URL:** https://discourse.paraview.org/t/flow-rate-specific-area/6846
**Category:** ParaView Support
**Created:** [April 2, 2021, 1:15am UTC](https://discourse.paraview.org/t/flow-rate-specific-area/6846 "2021-04-02T01:15:03Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![mylee](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/m/df705f/32.png) [@mylee](https://discourse.paraview.org/u/mylee)
#### Post date: [April 2, 2021, 1:15am UTC](https://discourse.paraview.org/t/flow-rate-specific-area/6846/1 "2021-04-02T01:15:03Z")

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Hello

i need to calculate mass flow rate of three outlet in one flow domain.  
i have no something to represent three outlet surface.  
so i cannot activate or choose the outlet surfaces alone.

so my idea was extract outlet surface and calculate flow rate with normal vector.  
but i have no idea about extracting my target outlet surface.

thank you for your comments in advance.

 ![image](https://discourse.paraview.org/uploads/default/original/2X/a/acbef72d13f3a49b608f3003708f2932c17d283a.jpeg)