ISO 13485 Sample Size: Confidence and Reliability Calculator
ISO 13485 does not give you a fixed sample size. It expects you to justify one with a documented, statistically valid rationale for inspection and for process validation. This calculator gives the confidence and reliability success-run number you can cite and shows how lot size and reliability move it.
Your numbers
Probability that the claim about the population is true.
Lowest conforming rate you want to demonstrate.
Used for the finite population adjustment.
Your results
Zero-failure success run sizing for attribute (pass/fail) data. If you allow failures, variable data, or a regulator-specific plan, confirm the method with a statistician and your validation procedure.
Sample size vs reliability at chosen confidence
Sweeps Reliability (proportion conforming) from 80 to 99.5, holding your other inputs fixed.
Validation records on your own servers
Optional: talk about searching test and validation history with a private on-premises AI.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Pick the confidence level, set the reliability you must demonstrate and enter the lot size if the population is small. The primary output is the number of units that must all pass. Write the confidence, reliability and the reasoning in your validation protocol. Risk drives the choice: higher-risk characteristics under your risk management file deserve higher confidence and reliability.
- Link the confidence/reliability pair to the hazard severity in your risk file
- Document the formula and the rationale in the protocol, not just the number
- Re-run it when the claimed reliability changes
The formula and common pairs
For pass/fail data with zero allowed failures, n = ln(1 - C) / ln(R), rounded up, where C is confidence and R is reliability. Common results: 90/90 needs 22 units, 95/90 needs 29, 95/95 needs 59, 99/95 needs 90 and 95/99 needs 299. If you allow one failure, the 95/90 plan rises to 46 and 95/95 to 93. More failures need a binomial calculation rather than this closed form.
Inspection sampling versus validation sampling
Lot acceptance inspection often uses an AQL table such as ANSI/ASQ Z1.4 or ISO 2859-1, which sets a sample size from lot size and an acceptable quality level. That controls producer risk on a lot, but it does not by itself prove process capability. Process validation (IQ, OQ, PQ) commonly uses confidence and reliability for attribute data, or tolerance intervals and capability indices for variable data. Pick the method based on what the claim is.
Common mistakes
Teams pick 30 units because it feels standard, with no link to risk. Others forget that the success run assumes independent, representative samples drawn across lots, operators and time, not a single batch built in one hour.
- Using one lot for a validation that claims ongoing process performance
- Applying the finite correction to justify a tiny sample on a small lot without a risk rationale
- Not documenting what happens if a unit fails
Frequently Asked Questions
What sample size does ISO 13485 require?
The standard does not state a number. It requires that sampling plans be statistically valid and justified, and that process validation methods and criteria be documented. The justification usually links back to risk.
What does 95/95 mean?
It means 95 percent confidence that at least 95 percent of the population conforms. With zero allowed failures, that needs 59 samples.
Can I use AQL for process validation?
AQL plans control lot acceptance and are weak evidence of process capability. For validation, regulators and notified bodies generally expect a rationale tied to confidence, reliability or capability, plus risk.
Does a smaller lot let me use fewer samples?
A finite correction can reduce the number, and with very small lots you may test everything. Document the reasoning and make sure the samples still represent the real variation.
If your inspection and test records sit in an ERP or quality system, Netray can add a private AI layer on-premises so engineers can query historical results when writing a sampling rationale. Get in touch if useful.
Related Tools
AQL Sample Size Calculator (ANSI Z1.4)
Find the Z1.4 sample size code letter and single sampling sample size for a lot, then see how likely the lot is to be accepted at a given defect rate.
Quality & InspectionMedical Device Success Run Validation Sample Size Calculator
Calculates the zero-failure sample size needed to claim a reliability at a confidence level, and splits it across your PQ lots.
Quality & InspectionZero Acceptance Sample Size Calculator (Confidence and Reliability)
Success-run sample size for c=0 plans: how many conforming pieces prove a reliability at a given confidence, with inspection time.
Quality & InspectionCost of ISO 13485 Certification Estimator
Estimate the cost for ISO 13485 certification across registrar audit days, consultant effort, training and internal time, for year one and the full three-year cycle.
More Quality & Inspection tools
See all- CAPA Corrective and Preventive Action Form Template
- Device History Record (DHR) Template
- ISO 13485 Internal Audit Checklist
- Process Validation IQ OQ PQ Template
- Medical Device Complaint Handling Form Template
- ISO 14971 Risk Management Worksheet
- Sterilization Load Record Template
- Medical Device Design Verification Protocol Template
- Medical Device Supplier Evaluation Scoring Worksheet
Keep exploring
Free tools
- ISO 13485 Document TemplatesAn editable ISO 13485 template set covering a quality manual outline, a software validation plan for ERP and quality software, and a supplier quality agreement.
- Medical Device Success Run Validation Sample Size CalculatorCalculates the zero-failure sample size needed to claim a reliability at a confidence level, and splits it across your PQ lots.
- ISO 13485 Quality Plan Template with Medical Device File ExampleA fill-in ISO 13485 quality plan with a medical device file content example and a clause compliance checklist table.
ERP fixes and how-tos
- SAP QM Sample Label Printing: How to Print Physical Sample LabelsHow SAP QM sample label printing works: physical samples on an inspection lot, the QPR print transactions, the form behind the label and printer checks.
- SAP QM Sample-Drawing Procedure: Setup and Use (QPV1)Set up an SAP QM sample-drawing procedure with QPV1: containers, number of samples, link to the inspection plan and lot, and how physical samples are created.
Guides
- ISO 13485 ERP Requirements for Medical Device Contract ManufacturersWhat ISO 13485 and FDA QMSR actually require of an ERP at a medical device contract manufacturer: records, traceability, change control and software validation.
- Pricing IQ/OQ/PQ Process Validation Into a Medical Device QuoteHow medical device contract manufacturers price process validation: IQ/OQ/PQ scope, sample sizes, protocol writing, re-validation triggers and billing.
- ISO 13485 Medical Injection Molding Validation: IQ, OQ and PQHow medical injection molders structure IQ, OQ, PQ validation under ISO 13485: equipment, process window, capability runs, lot traceability and ERP records.
AI on your ERP
- AI on Your ERP for Medical Device Manufacturing Under QMSR and ISO 13485Private AI on your ERP for medical device makers: DHR assembly, UDI, complaints, CAPA and supplier controls under FDA QMSR and ISO 13485, kept on your own infrastructure.
- AI on Infor SyteLine for Medical Device Manufacturers: Genealogy, DHR and Audit EvidencePrivate AI on Infor SyteLine for medical device makers: lot and serial genealogy, DHR assembly, UDI and QMSR evidence, with human approval on every write.
Manufacturing hubs
- Medical Device Manufacturing in Minneapolis-St. PaulMedical device manufacturing in Minneapolis-St. Paul: ecosystem, FDA and ISO 13485 requirements, and ERP, quoting and document problems contract makers face.
- MDMA, AdvaMed and medical device manufacturing: regulation, ERP and AI realitiesMDMA and AdvaMed medical device manufacturing: FDA QMSR, ISO 13485, UDI and EU MDR, plus the ERP, traceability and private AI issues device makers face.