--- title: "Process Capability (Cp/Cpk) and SPC… | MedTech Terms" description: "Statistical metrics and methods for monitoring whether a process meets its specifications. Plain-English Manufacturing definition for MedTech teams, with exampl" lang: en json-ld: | { "@context": "https://schema.org", "@graph": [ { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/spc-cpk#term", "name": "Process Capability (Cp/Cpk) and SPC", "description": "Statistical Process Control (SPC) uses control charts to monitor process stability. Process capability indices Cp and Cpk quantify how well a stable process fits within specification limits, with Cpk accounting for centering.", "url": "https://medtechterms.com/terms/spc-cpk", "termCode": "spc-cpk", "inDefinedTermSet": { "@type": "DefinedTermSet", "name": "MedTech Terms", "url": "https://medtechterms.com/terms" } }, { "@type": "Article", "@id": "https://medtechterms.com/terms/spc-cpk#article", "headline": "Process Capability (Cp/Cpk) and SPC", "description": "Statistical metrics and methods for monitoring whether a process meets its specifications.", "url": "https://medtechterms.com/terms/spc-cpk", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://medtechterms.com/terms/spc-cpk" }, "about": { "@id": "https://medtechterms.com/terms/spc-cpk#term" }, "articleSection": "Manufacturing", "inLanguage": "en", "keywords": "Process Capability (Cp/Cpk) and SPC, 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": "GHTF 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": "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" } }, { "@type": "CreativeWork", "name": "ISO 13485 Standard Page", "url": "https://www.iso.org/iso-13485-medical-devices.html", "publisher": { "@type": "Organization", "name": "ISO" } } ], "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/qsr#term", "name": "Quality System Regulation", "alternateName": "QSR / 21 CFR 820", "url": "https://medtechterms.com/terms/qsr" }, { "@type": "DefinedTerm", "@id": "https://medtechterms.com/terms/iso-13485#term", "name": "ISO 13485", "url": "https://medtechterms.com/terms/iso-13485" } ] }, { "@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 (Cp/Cpk) and SPC", "item": "https://medtechterms.com/terms/spc-cpk" } ] }, { "@type": "FAQPage", "@id": "https://medtechterms.com/terms/spc-cpk#faq", "mainEntity": [ { "@type": "Question", "name": "What is the primary difference between Cp and Cpk?", "acceptedAnswer": { "@type": "Answer", "text": "Cp assesses the potential capability of a process based on its spread relative to specification limits, assuming the process is perfectly centered. Cpk, on the other hand, considers both the process spread and its centering, providing a more realistic measure of actual process capability by accounting for how close the process mean is to the nearest specification limit." } }, { "@type": "Question", "name": "Why are specific Cpk targets, like 1.33 or 1.67, recommended in MedTech?", "acceptedAnswer": { "@type": "Answer", "text": "These Cpk targets are generally accepted industry benchmarks that correlate with a very low probability of producing defects, thereby ensuring high product quality and patient safety. A Cpk of 1.33 implies that the process mean is at least four standard deviations from the nearest specification limit, while 1.67 implies five standard deviations, crucial for safety-critical medical devices." } }, { "@type": "Question", "name": "How does SPC relate to process validation?", "acceptedAnswer": { "@type": "Answer", "text": "SPC is a critical tool used during process validation to demonstrate that a process is stable and in a state of control. Continued monitoring with SPC after validation helps maintain this state of control, ensuring ongoing conformance to requirements as mandated by regulatory bodies for the entire product lifecycle." } } ] } ] } --- [ 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 (Cp/Cpk) and SPC [All terms](/terms) Manufacturing [Quality System](/ecosystems/quality-system)[Manufacturing & Supply](/ecosystems/manufacturing-supply) # Process Capability (Cp/Cpk) and SPC Statistical metrics and methods for monitoring whether a process meets its specifications. Reviewed by [Christian Espinosa, Founder, Blue Goat Cyber](/authors/christian-espinosa) Last reviewed May 5, 2026 ## Definition Statistical Process Control (SPC) uses control charts to monitor process stability. Process capability indices Cp and Cpk quantify how well a stable process fits within specification limits, with Cpk accounting for centering. What the regulation says The FDA, in its guidance on [Process Validation](/terms/process-validation) General Principles and Practices, expects manufacturing processes to be in a state of control and capable of consistently producing conforming product. This aligns with quality system regulations like 21 CFR Part 820.75, which requires that process control procedures be established and maintained to ensure that a device conforms to its specifications. International standards such as [ISO 13485](/terms/iso-13485) also emphasize the importance of process control and validation to ensure product safety and effectiveness. ## What this means in practice [Process validation](/terms/process-validation) per the FDA/GHTF guidance expects capable and stable processes. Common medical-device targets are Cpk ≥ 1.33 for routine attributes and ≥ 1.67 for safety-critical ones. ## Examples - A manufacturer monitors the sterilization cycle temperature using SPC control charts to ensure it remains within validated limits, preventing under-sterilization. The Cpk of the temperature distribution is calculated to confirm its capability. If the control chart shows an out-of-control point, an investigation is initiated. - During the molding of an orthopedic implant, critical dimensions are tracked with SPC. The Cpk for these dimensions must meet the specified 1.67 target for safety-critical features, demonstrating that the process consistently produces parts within tolerance. - A pharmaceutical company uses SPC to monitor the fill volume of a liquid drug product. Control charts detect shifts in the mean fill volume, and the Cpk value indicates the process capability to meet label claims and avoid over/under-filling. Common pitfalls - • A common pitfall is calculating Cpk on unstable processes, leading to misleading capability assessments. - • Misinterpreting a high Cpk value as a guarantee of product quality without considering other factors like measurement system variability is a mistake. - • Failing to regularly monitor and react to SPC control chart signals can lead to process drift and non-conforming products. - • Only focusing on Cpk without attention to critical process parameters and their clinical impact is a pitfall. - • Setting arbitrary Cpk targets without a rational basis tied to risk assessment and product requirements can lead to inefficient resource allocation or inadequate quality control. ## Frequently asked questions What is the primary difference between Cp and Cpk? Cp assesses the potential capability of a process based on its spread relative to specification limits, assuming the process is perfectly centered. Cpk, on the other hand, considers both the process spread and its centering, providing a more realistic measure of actual process capability by accounting for how close the process mean is to the nearest specification limit. Why are specific Cpk targets, like 1.33 or 1.67, recommended in MedTech? How does SPC 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)[ Standards ISO 13485 International standard for medical device quality management systems. ](/terms/iso-13485)[ Quality & Risk Quality System Regulation(QSR / 21 CFR 820) FDA's current good manufacturing practice (cGMP) requirements for medical devices. ](/terms/qsr) ### 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 GHTF· 1 FDA· 1 ISO· 1 1. [1 GHTF Process Validation Guidance Verified 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) 2. [2 FDA - Device Manufacturing Verified FDA · fda.gov ](https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance/postmarket-requirements-devices) 3. [3 ISO 13485 Standard Page Verified ISO · iso.org ](https://www.iso.org/iso-13485-medical-devices.html) 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=spc-cpk) Learn in 60 seconds Card Lesson Quiz Statistical metrics and methods for monitoring whether a process meets its specifications. - · Process validation per the FDA/GHTF guidance expects capable and stable processes. - · Common medical-device targets are Cpk ≥ 1.33 for routine attributes and ≥ 1.67 for safety-critical ones. - · Process capability indices Cp and Cpk quantify how well a stable process fits within specification limits, with Cpk accounting for centering. Remember this Watch out: A common pitfall is calculating Cpk on unstable processes, leading to misleading capability assessments. Related terms - [Process Validation ](/terms/process-validation) - [Quality System Regulation(QSR / 21 CFR 820) ](/terms/qsr) - [ISO 13485 ](/terms/iso-13485) You may also need Auto-suggested from Manufacturing and shared keywords. - [Process Capability and Cpk ](/terms/process-capability-cpk) - [Algorithm Change Protocol(ACP) ](/terms/algorithm-change-protocol) - [IQ / OQ / PQ ](/terms/iq-oq-pq) - [Bioburden ](/terms/bioburden) - [Container Closure Integrity(CCI) ](/terms/container-closure) - [Device Master Record(DMR) ](/terms/dmr) [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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