Normal Inspection Plan Calculator

Turn quality targets into practical sampling decisions. Adjust risks, lot size, and defect assumptions easily. Get accept or reject guidance in seconds, consistently now.

Calculator

Choose whether to design a plan from risk targets, or evaluate an existing plan. The layout adapts to three columns on large screens, two on smaller, and one on mobile.

Design finds the smallest plan meeting your risk targets.
Finite lot uses lot size in the probability calculation.
Total units in the lot you want to accept or reject.
“Good lot” quality you want to accept most of the time.
“Bad lot” quality you want to reject most of the time.
Enter after you inspect to get an accept/reject decision.
Chance of rejecting a good lot at AQL.
Chance of accepting a bad lot at RQL/LTPD.
Higher values broaden the search, but may be slower.
Increase if no plan is found with your risk targets.
How many units you inspect.
Accept the lot when observed defects are ≤ c.
Controls how expected defectives are converted to integers.

Example data table

Typical settings shown below use α=5% and β=10% with the large-lot model.
Lot size (N) AQL (%) RQL/LTPD (%) α (%) β (%) Sample n Accept c
500 1.00 7.00 5.00 10.00 75 2
2000 0.65 5.00 5.00 10.00 105 2
10000 0.40 3.00 5.00 10.00 176 2

Formula used

The plan is a single-sample acceptance rule: inspect n units, count defects x, and accept the lot when x ≤ c.

  • Acceptance probability (binomial): P(accept | p) = Σk=0..c [ C(n,k) pk (1−p)n−k ]
  • Acceptance probability (finite lot): P(accept | D) = Σk=0..c [ C(D,k) C(N−D,n−k) / C(N,n) ]
  • Design constraints: choose the smallest (n,c) meeting P(accept | AQL) ≥ 1−α and P(accept | RQL/LTPD) ≤ β.

In the finite-lot model, defectives are approximated as D ≈ p × N and rounded per your selection.

How to use this calculator

  1. Pick Design a plan to compute an inspection plan from targets.
  2. Enter your lot size, AQL, and RQL/LTPD.
  3. Set α (rejecting good lots) and β (accepting bad lots).
  4. Submit to get n, c, and acceptance probabilities.
  5. After inspecting, enter observed defects to receive a decision.

If no plan is found, increase the search limits or relax risk targets.

Related Calculators

AQL Sample SizeAcceptance Sampling PlanLot Size CalculatorInspection Level SelectorRandom Sample GeneratorSampling Plan FinderDouble Sampling PlanSwitching Rules ToolInspection Severity SelectorAQL Lookup Table

Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.