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AQL sampling plan template

An AQL sampling plan tells an inspector how many pieces to check from a lot and how many defects the lot can have and still be accepted. AQL stands for acceptable quality limit: the defect rate that a lot can have and still be accepted most of the time. In a single sampling plan you take a random sample of a set size, count the defects, and accept the lot if the count is at or below the accept number or reject it if the count reaches the reject number. This template has a one-page guide for choosing the sample size from the lot size and the inspection level, a table of accept and reject numbers for the common AQL values, an inspection record for critical, major and minor defects, and a worked example. The Excel version looks up the plan for you, decides accept or reject in a log, and summarises lots by supplier. The plans are calculated for this template and are close to, not copies of, the tables in published sampling standards; if your contract names a standard, use its tables.

Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.

Page 1 of the AQL sampling plan templateA table of sample sizes by lot size band and inspection level I, II and III, beside numbered steps for choosing a plan and a table of critical, major and minor defect classes.
Sample size by lot size and levelAccept and reject numbers for 11 AQLsCritical, major and minor classesInspection recordLookup in ExcelAccept or reject decision logSummary by supplierWorked example
Filled-in AQL sampling plan template: a lot of 3,000 connectors rejected on majors
The same sheet filled in with the worked example (page 4 of the PDF, illustrative numbers). Open full size (opens the picture in a new tab)

When to use it

When to use an AQL sampling plan

  • For incoming inspection of purchased parts when checking every piece costs too much or would damage the parts.
  • For final inspection of a lot before it ships, when 100% inspection is not practical.
  • To record the sample size, the defects found by class and the decision for each lot in one place.
  • To show a supplier how many lots were accepted and rejected over a month.
  • Not when a contract names a sampling standard and its tables: use that standard's tables for those lots.

How to fill it in

  1. 1

    Class the defects

    Decide what counts as critical, major and minor for the part. Critical defects could hurt someone or break a requirement and reject the lot on sight. Major defects stop the part working. Minor ones do not affect use.

  2. 2

    Choose the AQL and the inspection level

    Give major and minor defects an AQL each. Use inspection level II unless there is a reason not to: level I when the supplier's record is good, level III when a miss is costly or the record is poor.

  3. 3

    Read the sample size

    Look up the lot size and the level in the sample size table. If the lot is no bigger than the sample, inspect every piece.

  4. 4

    Read the accept and reject numbers

    In the accept and reject table, find the row for the sample size and the column for each AQL. The reject number is one more than the accept number.

  5. 5

    Draw the sample and count the defects

    Take the sample at random across the whole lot, not from the top box, and inspect every piece in it. Tally the defects by class.

  6. 6

    Decide and record

    The lot is accepted only if every class is at or below its accept number. Otherwise reject it, choose a disposition and raise a report to the supplier.

A filled-in example

Illustrative, not a benchmark

An example (illustrative): a lot of 3,000 connectors from a made-up supplier, inspected at general level II with a major AQL of 1.0 and a minor AQL of 2.5.

  • A lot of 3,000 falls in the 1,901 to 4,700 band, so level II gives a sample of 125 connectors.
  • For a sample of 125, the major plan at AQL 1.0 accepts up to 3 defects and rejects at 4. The minor plan at AQL 2.5 accepts up to 6 and rejects at 7. Any critical defect rejects the lot.
  • The inspector finds 0 critical, 4 major (three loose crimps and a bent pin) and 2 minor (scuffed housings).
  • Four majors reach the reject number, so the lot is rejected on majors even though it passes on minors.

The lot is returned to the supplier and a corrective action request is made. Over the month, 12 lots were inspected from five suppliers: 8 accepted and 4 rejected.

Common mistakes

  • Treating the AQL as a target

    An AQL of 1.0 does not mean 1% defects is fine. It means a lot at that rate is accepted most of the time. A lot at the AQL still has defects in it.

  • Sampling from the top of the pile

    A sample from the most convenient boxes tells you about those boxes. Draw it across the whole lot and across all the containers.

  • Fixing the count to pass the lot

    Re-inspecting a rejected lot until it passes defeats the plan. If you doubt the decision, use a larger sample or escalate it, and record what you did.

  • Using one AQL for every kind of defect

    Critical, major and minor defects need different limits. Setting a single AQL lets a serious defect hide among cosmetic ones.

  • Using these plans when a contract names a standard

    These plans are calculated for this template. If a customer or contract names a published sampling standard, use that standard's tables for those lots.

Download the template

Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.

Run this template in LeanSuite

In LeanSuite, when an inspector flags a defect the batch is quarantined and a SCAR with photos goes to Quality and Procurement, and the SCAR's lifecycle, including the days the supplier took to respond, feeds the supplier's scorecard.

See it in a 45-minute demo

FAQ

AQL sampling plan template: common questions

  1. AQL stands for acceptable quality limit. It is the defect rate that a lot can have and still be accepted most of the time under a sampling plan. It is not a target for quality and not a promise that parts are good.

  2. From the lot size and the inspection level. Larger lots get larger samples, and level III uses a bigger sample than level II for the same lot. This template gives a table for levels I, II and III; if your contract names a standard, use its table.

  3. A critical defect could hurt someone or break a legal or safety requirement. A major defect stops the part working or makes it unusable. A minor defect is a departure that does not affect function or use. Each class gets its own limit.

  4. The accept number is the most defects you can find in the sample and still accept the lot for that class. The reject number is the count at which you reject it. In a single sampling plan the reject number is the accept number plus one.

  5. No. The plans are calculated for this template from the binomial distribution and are close to, but not copies of, published sampling tables. If a customer or contract names a standard, use that standard's tables for those lots.

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