GIFSQ Tools · Module 4 — Microbiology Methods & Laboratory Operations · Tool 71 of 500
Build an ICMSF 2-class or 3-class attribute sampling plan (n, c, m, M) and test a lot against it from the observed sample counts.
Try sample values — fills the form with the worked example below.
Saved sampling plans
Saved on this device only. Calculate a result first, then add it to the log.
| Date / time | Plan | n | c | m | M | Above m | Above M | Decision |
|---|
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Lot decision
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Marginal samples (m to M)
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Samples above m (%)
Equation: 3-class plan: accept the lot when no sample exceeds M and at most c samples fall between m and M. 2-class plan: accept when at most c samples exceed m. Marginal count = samples above m minus samples above M.
Method: ICMSF 2-class and 3-class attribute sampling plans, as used in the ICMSF sampling-plan tables and ISO 2859-1 attribute sampling. The plan class, n, c, m and M are set from the product specification or the applicable microbiological criteria.
Assumptions: samples are drawn at random from the lot; each sample unit is independent; the counts entered are the laboratory results for the n units.
Limitations: an attribute plan judges the lot only on the samples tested — a passed lot can still contain defective units, and the plan says nothing about the level of contamination below m. It does not replace a full risk assessment.
Rounding: percentages to 1 decimal place. Counts are whole numbers and are never rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: ICMSF 2-class and 3-class attribute sampling plans, as used in the ICMSF sampling-plan tables and ISO 2859-1 attribute sampling. The plan class, n, c, m and M are set from the product specification or the applicable microbiological criteria.
Assumptions: samples are drawn at random from the lot; each sample unit is independent; the counts entered are the laboratory results for the n units.
Limitations: an attribute plan judges the lot only on the samples tested — a passed lot can still contain defective units, and the plan says nothing about the level of contamination below m. It does not replace a full risk assessment.
Rounding: percentages to 1 decimal place. Counts are whole numbers and are never rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 3-class plan, n = 5, c = 2, m = 100 CFU/g, M = 1000 CFU/g; 2 samples above m and none above M. Marginal count = 2, which is within c = 2, and no sample exceeds M, so the lot is accepted; 40.0 % of samples were above m.
Enter values above to see results.
Typical ICMSF plans: n = 5, c = 2 for many ready-to-eat foods; n = 5, c = 0 for higher-risk products. Always take n, c, m and M from the applicable specification, not from this tool. Tool 71 of 500 — GIFSQ
