Inspection Level Selector Calculator

Calculator Inputs

Lot Size

AQL (%)

Expected Defect Rate (%)

Process Capability (Cpk)

Supplier Score (0-100)

Failure Severity (1-10)

Incoming Variability (1-10)

Estimated Failure Cost

Inspection Cost per Unit

Historical Escapes (PPM)

Confidence Target (%)

Criticality

Inspection Stage

Destructive Test Required?

Reset

Example Data Table

Lot Size	AQL	Expected Defect %	Cpk	Supplier Score	Criticality	Suggested Level	Code Letter	Sample Size	State
600	1.0%	0.7%	1.72	94	Medium	I	G	32	Reduced
2500	1.0%	1.8%	1.25	78	High	II	K	125	Tightened
12000	0.65%	2.4%	0.96	61	Critical	III	N	500	Tightened

Formula Used

1) Weighted risk score
Risk Score = 100 × (weighted defect, history, capability, supplier, severity, variability, cost, and confidence factors) × criticality multiplier × stage multiplier.

2) Inspection family and level
General levels are used for most sampling. Special levels are favored when testing is destructive and total risk is still moderate.

3) Code letter lookup
The calculator maps lot size and selected level to a sample size code letter using a built-in acceptance-sampling lookup structure.

4) Sample size
Sample Size = code letter sample quantity, capped at lot size.

5) Acceptance numbers
Base Accept = round(Sample Size × AQL). Tightened lowers acceptance by one. Reduced raises acceptance by one.

6) Detection confidence
Detection Confidence = 1 − (1 − defect rate)^{sample size}.

7) Acceptance probability
Acceptance probability is estimated with a Poisson approximation using the selected sample size and the allowed defect threshold.

How to Use This Calculator

Enter the lot size you plan to inspect.
Set the target AQL for the product or customer requirement.
Add the expected defect rate based on current performance.
Enter process capability, supplier score, and historical escape level.
Score severity and variability from 1 to 10.
Enter inspection cost and failure cost to reflect business impact.
Choose criticality, stage, and whether the test is destructive.
Submit the form to see the suggested inspection family, level, code letter, sample size, and acceptance limits.
Review the graph to compare sample burden and detection confidence across levels.
Use the CSV and PDF buttons to export the result for quality records.

FAQs

1. What does this calculator actually select?

It recommends an inspection family, level, state, code letter, and sample size using lot size, risk indicators, and expected quality performance.

2. When should I use special inspection levels?

Use special levels when tests are destructive, costly, or slow, and when a smaller sample still provides enough operational control.

3. Why does a higher risk score increase inspection intensity?

Higher risk means defects are more likely or more harmful. The calculator responds by recommending broader sampling or a tighter inspection state.

4. Is this a replacement for customer or regulatory standards?

No. It is a decision-support tool. Always follow contract terms, industry rules, and internal procedures when those are stricter.

5. What does detection confidence mean?

It estimates the chance of finding at least one defect in the sample when the entered defect rate is true across the lot.

6. Why can reduced inspection still be recommended?

Reduced inspection appears when supplier performance is strong, capability is stable, and historical escapes are low enough to justify lower sampling burden.

7. How should I score severity and variability?

Use higher severity for defects with bigger customer, safety, or compliance impact. Use higher variability for unstable or inconsistent incoming quality.

8. Can I use this for incoming, in-process, and final inspection?

Yes. The stage selector slightly adjusts the risk model so you can compare inspection intensity across different quality checkpoints.