##  [Surface Roughness (Ra)](/surface-roughness-ra) 

  ##  [Surface Roughness (Ra)](https://engineering.quantumdictionary.io/surface-roughness-ra-0) 

  

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**Engineering & Applied Technologies Dictionary**

 







 

 

 

 



 

 

 

 

Definition

The arithmetic average roughness Ra is the arithmetic mean of the absolute values of vertical deviations of a real surface profile from its mean line over a specified sampling length; expressed in units of length (e.g., μm), Ra quantifies average micro‑texture but does not capture peak height distribution, spacing, or functional features relevant to sealing, friction or fatigue initiation.