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Inspection Sample Size Calculator

Work out inspection sample size instantly with clear inputs, formula shown and shareable results.

About Inspection Sample Size Calculator

Attribute sampling draws a sample whose size grows with the square root of lot size, scaled by inspection level, and accepts the lot if defects found do not exceed the acceptance number derived from the AQL. Tightened inspection uses larger samples, reduced inspection smaller ones, which is how switching rules reward or punish supplier history.

Formulas

Sample size

Sample = sqrt(lot size) x level factor (I 0.4, II 1.0, III 1.6)

Acceptance

Acceptance number = floor(sample size x AQL % / 100); accept if defects <= acceptance number

Worked example

With the default values below, Inspection Sample Size Calculator returns Sample Size of 71. Change any input above and every figure here is recalculated in your browser.

Inputs used

Lot Sizeminimum 1
5,000
Inspection Levelone of Level I (reduced), Level II (normal), Level III (tightened)
Level II (normal)
Acceptable Quality Limitaccepts 0.01–20 %
2.5 %
Defects Found In Sampleminimum 0
3

Results

Sample Size
71
Acceptance Number
1
Rejection Number
2
Lot Decision
Reject the lot

Step by step

  1. 1Values used
  2. 2Sample size
  3. 3Acceptance
  4. 4Sample Size= 71
  5. 5Acceptance Number= 1
  6. 6Rejection Number= 2
  7. 7Lot Decision= Reject the lot

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Sampling plans used for contractual or regulatory acceptance must follow the published standard tables and switching rules. Use this as a planning approximation only.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Sampling plans used for contractual or regulatory acceptance must follow the published standard tables and switching rules. Use this as a planning approximation only.

Frequently Asked Questions

Is this the same as the published sampling tables?

It approximates them. For contractual or regulatory acceptance always use the actual code letter and table from the applicable standard rather than an approximation.

Does AQL mean defects are acceptable?

No. AQL is the quality level a sampling plan will routinely accept, not a target. Producing at AQL guarantees regular rejections, because the plan is designed to accept better-than-AQL lots.

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