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SPC 101: Differentiating Between Cpk and Ppk Values

By Grace Barton Updated
SPC 101: Differentiating Between Cpk and Ppk Values

Let’s take the confusion out of Cpk and Ppk.

Just like control charts tell us about the stability of the process, capability analyses tell us about process capability. Capability Indices help us judge whether the process is capable of producing parts that are within specifications.

Among the various capability indices, Cpk and Ppk are popular in the manufacturing world. However, many users report they are also the most confusing.

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These two indices consider process centering to calculate the process capability.

The formula for the Cpk and Ppk are:

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So which capability index should you use, Cpk or Ppk? Although they show similar information, they have slightly different uses.

Cpk uses an “estimated sigma” value in its formula. It is commonly used to measure whether the process is capable of meeting a customer’s requirements.

Ppk uses the “actual sigma” value in its formula so it is commonly used to measure whether the process is actually meeting a customer’s requirements.

Beena Anand
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Grace Barton

Marketing Specialist

About the Author Latest Posts

Grace Barton is a digital marketing and competitive intelligence professional who crafts strategic narratives by bridging marketing insights with analytical expertise. At Advantive, she creates engaging, data-driven content tailored to the distribution, manufacturing, packaging, and quality industries. Her goal is to deliver impactful messaging that drives engagement and growth based on specific gap closure needs, whether responding to sales organization requirements, pinpointing gaps in content, or meeting immediate market trends.
She thrives on transforming competitive intelligence into actionable insights for the sales organization. Grace manages Advantive’s competitive intelligence platform, Klue, to equip the sales team with the battlecards and market data they need to stay ahead of competitors. Since launch, she’s built 28+ battlecards across four lines of business, ensuring the GTM strategy stays sharp.
Grace has a passion for leveraging market insights with storytelling to guide strategic decision-making, empower sales organizations, and nurture organizational growth.

Areas of Expertise: Digital Marketing, Competitive Intelligence, Strategic Narratives, Marketing Insights, Analytical Expertise

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