--- title: "Process Capability and Cpk, Definition | MedTech Terms" description: "Statistical measures (Cp, Cpk, Pp, Ppk) of how well a process output fits within specification limits. Plain-English Manufacturing definition for MedTech teams," lang: en json-ld: | { "@context": "https://schema.org", "@graph": [ { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/process-capability-cpk#term", "name": "Process Capability and Cpk", "description": "Cpk relates the distance between the process mean and the nearest spec limit to process variation. Cpk ≥ 1.33 is a common minimum target for critical characteristics; ≥ 1.67 for safety-critical attributes.", "url": "https://medtechterms.com/terms/process-capability-cpk", "termCode": "process-capability-cpk", "inDefinedTermSet": { "@type": "DefinedTermSet", "name": "MedTech Terms", "url": "https://medtechterms.com/terms" } }, { "@type": "Article", "@id": "https://medtechterms.com/terms/process-capability-cpk#article", "headline": "Process Capability and Cpk", "description": "Statistical measures (Cp, Cpk, Pp, Ppk) of how well a process output fits within specification limits.", "url": "https://medtechterms.com/terms/process-capability-cpk", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://medtechterms.com/terms/process-capability-cpk" }, "about": { "@id": "https://medtechterms.com/terms/process-capability-cpk#term" }, "articleSection": "Manufacturing", "inLanguage": "en", "keywords": "Process Capability and Cpk, Manufacturing, medical device, MedTech", "author": { "@type": "Person", "name": "Christian Espinosa", "jobTitle": "Founder, Blue Goat Cyber", "url": "https://bluegoatcyber.com" }, "publisher": { "@type": "Organization", "name": "MedTech Terms", "url": "https://medtechterms.com" }, "isPartOf": { "@type": "WebSite", "name": "MedTech Terms", "url": "https://medtechterms.com" }, "datePublished": "2026-05-05", "dateModified": "2026-05-05", "citation": [ { "@type": "CreativeWork", "name": "AIAG SPC Manual", "url": "https://www.aiag.org/", "publisher": { "@type": "Organization", "name": "AIAG" } }, { "@type": "CreativeWork", "name": "GHTF/IMDRF Process Validation Guidance", "url": "https://www.imdrf.org/sites/default/files/docs/ghtf/final/sg3/technical-docs/ghtf-sg3-n99-10-2004-qms-process-guidance-04010.pdf", "publisher": { "@type": "Organization", "name": "IMDRF/GHTF" } }, { "@type": "CreativeWork", "name": "FDA - Device Manufacturing", "url": "https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance/postmarket-requirements-devices", "publisher": { "@type": "Organization", "name": "FDA" } } ], "mentions": [ { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/process-validation#term", "name": "Process Validation", "url": "https://medtechterms.com/terms/process-validation" }, { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/scrap-yield#term", "name": "Scrap Rate and Yield", "url": "https://medtechterms.com/terms/scrap-yield" } ] }, { "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://medtechterms.com/" }, { "@type": "ListItem", "position": 2, "name": "Terms", "item": "https://medtechterms.com/terms" }, { "@type": "ListItem", "position": 3, "name": "Manufacturing", "item": "https://medtechterms.com/terms?cat=Manufacturing" }, { "@type": "ListItem", "position": 4, "name": "Process Capability and Cpk", "item": "https://medtechterms.com/terms/process-capability-cpk" } ] }, { "@type": "FAQPage", "@id": "https://medtechterms.com/terms/process-capability-cpk#faq", "mainEntity": [ { "@type": "Question", "name": "What is the difference between PpK and Cpk?", "acceptedAnswer": { "@type": "Answer", "text": "PpK (Process Performance Index) assesses the overall capability of a process based on preliminary data, reflecting its potential performance. Cpk (Process Capability Index) evaluates the sustained performance of a stable process over time, generally after it has been brought under statistical control." } }, { "@type": "Question", "name": "Why is Cpk ≥ 1.33 a common target?", "acceptedAnswer": { "@type": "Answer", "text": "A Cpk of 1.33 corresponds to a process where the nearest specification limit is at least four standard deviations from the process mean, indicating a high probability of conforming product. This target is widely adopted in industries like MedTech to ensure a low defect rate and robust process performance. For safety-critical attributes, higher Cpk targets, such as 1.67 or 2.0, are often mandated to provide an even greater margin of safety and reduce the risk of patient harm." } }, { "@type": "Question", "name": "How does Cpk relate to process validation?", "acceptedAnswer": { "@type": "Answer", "text": "During process validation, Cpk is frequently used to provide objective evidence that a manufacturing process will consistently produce a product that meets its predetermined specifications. It helps confirm that the process is stable, capable, and predictable, which is a key requirement of 21 CFR 820.75 for process validation and revalidation." } } ] } ] } --- [ MedTech Terms The authoritative reference ](/) Browse Learn [Latest](/latest) About 1. [Home](/) 2. / 3. [Terms](/terms) 4. / 5. [Manufacturing](/terms?cat=Manufacturing) 6. / 7. Process Capability and Cpk [All terms](/terms) Manufacturing [Quality System](/ecosystems/quality-system)[Manufacturing & Supply](/ecosystems/manufacturing-supply) # Process Capability and Cpk Statistical measures (Cp, Cpk, Pp, Ppk) of how well a process output fits within specification limits. Reviewed by [Christian Espinosa, Founder, Blue Goat Cyber](/authors/christian-espinosa) Last reviewed May 5, 2026 ## Definition Cpk relates the distance between the process mean and the nearest spec limit to process variation. Cpk ≥ 1.33 is a common minimum target for critical characteristics; ≥ 1.67 for safety-critical attributes. What the regulation says Process capability, often expressed as Cpk, is a statistical measure required by regulatory bodies like the FDA in 21 CFR 820.250 for [process validation](/terms/process-validation) activities. It demonstrates that a process is capable of consistently producing conforming product within specified limits. The EU [MDR](/terms/mdr-reporting), while not citing Cpk directly, mandates similar statistical techniques for verifying process control in Annex I, Section 3, related to [general safety and performance requirements](/terms/gspr). ## What this means in practice PPAP, supplier scorecards, and [process validation](/terms/process-validation) routinely use Cpk as a lever; 'Cpk theater' (manipulated samples) is a recurring audit concern. ## Examples - A manufacturer uses Cpk to demonstrate that its sterile packaging sealing process consistently maintains seal integrity within specified aesthetic and functional limits, supporting the sterility assurance level of the device. - During a design transfer activity, an engineering team uses Cpk analysis to confirm that a new automated assembly line can consistently achieve the dimensional tolerances required for a critical implant component. - A quality engineer tracks Cpk for the fill volume of a liquid drug product to ensure that each vial contains the correct dosage, adhering to pharmacopeial requirements and patient safety considerations. Common pitfalls - • Using Cpk as the sole metric for process control without considering historical data or other statistical process control tools can be misleading. - • Manipulating samples to achieve a favorable Cpk without actual process improvement constitutes "Cpk theater" and can lead to non-conformances during audits. - • Assuming a good Cpk guarantees product quality without addressing potential sources of variation or measurement system analysis is a common error. - • Failing to establish appropriate Cpk targets based on risk and product criticality can result in inadequate process control for critical attributes. - • Not periodically re-evaluating Cpk after process changes or over time can lead to a loss of process control without detection. ## Frequently asked questions What is the difference between PpK and Cpk? PpK (Process Performance Index) assesses the overall capability of a process based on preliminary data, reflecting its potential performance. Cpk (Process Capability Index) evaluates the sustained performance of a stable process over time, generally after it has been brought under statistical control. Why is Cpk ≥ 1.33 a common target? How does Cpk relate to process validation? ## Related terms Grouped by theme ### Editor's picks · Hand-selected related concepts [ Manufacturing Process Validation Establishing documented evidence that a process consistently produces conforming output. ](/terms/process-validation)[ Manufacturing Scrap Rate and Yield Production metrics tracking material loss (scrap) and the proportion of acceptable output (yield). ](/terms/scrap-yield) ### More in Manufacturing · Same category [ Manufacturing Bill of Materials(BOM) Structured list of every component, sub-assembly, and quantity needed to manufacture a device. ](/terms/bom)[ Manufacturing Bioburden Quantification of viable microorganisms on or in a product before sterilization. ](/terms/bioburden)[ Manufacturing Cleanroom Classes (ISO 14644) ISO 14644 classification of cleanrooms by airborne particulate cleanliness (ISO 1 through ISO 9). ](/terms/cleanroom-iso-14644)[ Manufacturing Container Closure Integrity(CCI) Demonstration that a sterile package maintains microbial barrier and contents integrity over the labeled shelf life. ](/terms/container-closure) Cited by Where this term appears across MedTech Terms. Ecosystems (2) - [Quality System](/ecosystems/quality-system) - [Manufacturing & Supply](/ecosystems/manufacturing-supply) ## Primary references 3 sources Link health: 3 verified · last checked 2026-06-20 AIAG· 1 IMDRF/GHTF· 1 FDA· 1 1. [1 AIAG SPC Manual Verified AIAG · aiag.org ](https://www.aiag.org/) 2. [2 GHTF/IMDRF Process Validation Guidance Verified IMDRF/GHTF · imdrf.org ](https://www.imdrf.org/sites/default/files/docs/ghtf/final/sg3/technical-docs/ghtf-sg3-n99-10-2004-qms-process-guidance-04010.pdf) 3. [3 FDA - Device Manufacturing Verified FDA · fda.gov ](https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance/postmarket-requirements-devices) Inline markers like \[1\] jump to the matching reference above. Sponsor note ### Production controls for connected devices? We help device manufacturers operationalize cybersecurity in design transfer, production, and supplier controls. [Book a 30-minute discovery session](https://go.bluegoatcyber.com/meetings/blue-goat-cyber/discovery-session) - No obligation - Expert-led from minute one - NDA available on request MedTech Terms is a community resource sponsored by [Blue Goat Cyber](https://bluegoatcyber.com). Definitions are independent of any vendor. On this term Category Manufacturing Sources 3 Updated 5/5/2026 [Compare with another term](/compare?a=process-capability-cpk) Learn in 60 seconds Card Lesson Quiz Statistical measures (Cp, Cpk, Pp, Ppk) of how well a process output fits within specification limits. - · PPAP, supplier scorecards, and process validation routinely use Cpk as a lever; 'Cpk theater' (manipulated samples) is a recurring audit concern. - · Cpk ≥ 1.33 is a common minimum target for critical characteristics; ≥ 1.67 for safety-critical attributes. Remember this Watch out: Using Cpk as the sole metric for process control without considering historical data or other statistical process control tools can be misleading. Related terms - [Process Validation ](/terms/process-validation) - [Scrap Rate and Yield ](/terms/scrap-yield) You may also need Auto-suggested from Manufacturing and shared keywords. - [Process Capability (Cp/Cpk) and SPC ](/terms/spc-cpk) - [IQ / OQ / PQ ](/terms/iq-oq-pq) - [Sterilization ](/terms/sterilization) - [Propensity Score Methods ](/terms/propensity-score) - [Cleanroom Classes (ISO 14644) ](/terms/cleanroom-iso-14644) - [Device History Record(DHR) ](/terms/dhr) [All Manufacturing terms](/terms?cat=Manufacturing) MedTech Terms An authoritative, plain-language reference for the regulatory, quality, cybersecurity, and software terms that shape modern medical devices. 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