Minimum number of Subgroups to assess Process Capability

[DJN]

What is considered to be the minimum number of subgroups to assess process capability? I have been using 20 but have now been informed that 25 should be used. Is this correct?

 

[M Greenaway]

The QS9000 SPC manual generally recommends at least 25 sub-groups.

 

[DJN]

Thanks for that.

 

[D.Scott]

Hi David - welcome to the Cove.

An automotive PPAP using an X-bar and R chart would require a minimum of 25 subgroups containing at least 100 consecutive samples.

Dave