AQL Calculator
Find the inspection code letter, sample size, and accept/reject limits for critical, major, and minor defects.
Calculator is for informational purposes only. Terms and Conditions
The embedded lookup is a normal, single-sampling planning implementation based on public-domain MIL-STD-105E tables; verify the exact current standard or contract governing your inspection.
Choose the inspection criteria
Inspection level controls the sample-size code letter; each defect class can use a different AQL criterion.
Enter the lot size
Lot size is the total number of units in the batch or shipment being evaluated.
The optional defect counts under Advanced Options can be used after inspection to check the entered results against the calculated limits.
AQL Inspection Plan
The largest required sample is shown first; class-specific sample sizes and Ac/Re limits follow.
Plan details
- Code letter—
Show calculation steps Review code-letter lookup, sample-plan resolution, thresholds, and limitations
- Enter valid values to see the complete calculation.
Method, Sources, and Assumptions
Current-standard context, embedded lookup basis, limitations, and verification requirements.
The embedded code-letter and common-AQL plan data are based on the public-domain MIL-STD-105E normal single-sampling tables. Current ISO 2859-1:2026 and ANSI/ASQ Z1.4 requirements must be checked separately before contractual use.
- This calculator implements normal, single-sampling lookup behavior for common AQL values 0.65, 1.0, 1.5, 2.5, 4.0, and 6.5.
- “Zero tolerance” is treated as Ac 0 / Re 1 on the nominal sample and is not represented as an AQL table value.
- If an arrow-resolved sample equals or exceeds the lot size, the calculator flags 100% inspection instead of pretending the normal sampling Ac/Re pair still governs.
- Inspection severity switching, double/multiple sampling, skip-lot rules, defect classification, and counting basis are outside this calculator and must follow the applicable procedure.
Calculator guide
AQL Calculator Guide: Sample Size, Ac/Re, and Inspection Levels
The AQL Calculator above determines an inspection code letter, the number of units to inspect, and the acceptance and rejection limits for critical, major, and minor defect classes. The minimum project-specific input is lot size; you also choose the inspection level and the AQL criteria that apply to the lot. The result is a sampling plan, not an estimate of the lot’s actual defect percentage.
AQL means Acceptance Quality Limit in current ISO terminology; it is also commonly searched online as “acceptable quality level.” The calculator uses a normal, single-sampling lookup procedure. Lot size and inspection level first determine a sample-size code letter; the selected AQL then determines the applicable sample plan and its acceptance number (Ac) and rejection number (Re). That distinction matters because an AQL of 2.5 is not calculated by simply allowing 2.5% of the sample to be defective.
- Primary input
- Lot size plus the inspection level and defect-class criteria
- Primary output
- Units to inspect, with code letter and Ac/Re limits
- Sampling scope
- Normal · Single sampling
How to Use the AQL Calculator
Use the tool to turn a defined inspection lot into a sample plan, then optionally enter the defect counts found during inspection. The calculator updates automatically; its default 5,000-unit example is illustrative and should be replaced before making a real quality decision.
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Enter the lot size
Use the number of units in the inspection lot or batch. The field accepts whole numbers from 2 units upward. The relevant lot is the population from which the sample will actually be selected, not an unrelated annual production quantity.
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Choose the inspection level
Select General I, II, or III, or Special S-1 through S-4. The inspection level changes the sample-size code letter. General II is loaded in the example state, but the correct choice comes from the governing procedure, customer requirement, supplier-quality agreement, or standard.
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Select critical, major, and minor criteria
The calculator provides a separate critical-defect criterion and major/minor AQL selectors. Its zero-tolerance critical option is explicitly treated as Ac 0 / Re 1 rather than as an ordinary “AQL 0” table entry. Major and minor selections use the supported common AQL values shown in the tool.
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Read the code letter, sample size, and Ac/Re limits
The primary result is the largest required sample among the active defect-class plans. The result details show the class-specific sample size and Ac/Re pair, which is important when an AQL table arrow resolves one class to a different sample plan.
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Optionally enter inspection results
Open Advanced Options and enter whole-number counts for critical, major, and minor defects found. Use the same counting basis as the governing inspection plan—for example, nonconforming units or individual nonconformities. The tool checks each entered count against the corresponding plan. Enter all three counts when you want the displayed overall ACCEPT or REJECT status rather than a partial result.
How the AQL Sampling Plan Is Determined
This is a table-driven acceptance-sampling procedure rather than a single percentage formula. The calculator resolves the plan in stages so that the lot-size code, sample size, and Ac/Re limits stay tied to the selected inspection conditions.
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Lot size and inspection level determine the code letter
Lot-size ranges are grouped into discrete bands. For a given band, the selected General or Special inspection level maps to a sample-size code letter such as J, K, L, or M. The letter is an index into the sampling plan; it is not itself a quality grade.
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The code letter establishes a nominal sample size
Each code letter corresponds to a nominal sample size. For example, code L corresponds to a 200-unit nominal sample in the calculator’s normal-plan table.
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The selected AQL determines the Ac/Re plan
The AQL table cell provides the acceptance and rejection numbers, or directs the plan toward another sample size. The calculator follows those direction changes rather than assuming that every AQL uses the original code letter’s nominal sample.
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Sample size changes in discrete steps
Sample size does not increase one-for-one with lot size. Two different lot sizes can fall within the same table band and therefore use the same code letter and nominal sample size. For example, a 5,000-unit and a 9,000-unit lot are both within the 3,201–10,000 General II band used by the calculator and therefore both map to code L before any AQL-specific plan resolution.
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A resolved sample can reach the entire lot
If the resolved table sample equals or exceeds the lot size, the calculator flags 100% inspection instead of presenting the normal sampling Ac/Re pair as though only a sample were being inspected. The final disposition rule must then come from the governing inspection procedure.
Worked AQL Example: 5,000-Unit Lot
The calculator’s example state uses a 5,000-unit lot, General Inspection Level II, a zero-tolerance critical policy, Major AQL 2.5, and Minor AQL 4.0. This combination shows how the code-letter lookup and class-specific acceptance limits fit together.
Lookup procedure
- A 5,000-unit lot at General Level II falls in the 3,201–10,000 lot-size band and maps to code letter L in the calculator’s embedded code-letter table.
- Code L corresponds to a nominal sample size of 200 units.
- The critical zero-tolerance policy uses Ac 0 / Re 1 on that sample.
- Major AQL 2.5 resolves to Ac 10 / Re 11 for the 200-unit sample.
- Minor AQL 4.0 resolves to Ac 14 / Re 15 for the 200-unit sample.
Result
Inspect 200 units · Code L
Critical: Ac 0 / Re 1. Major AQL 2.5: Ac 10 / Re 11. Minor AQL 4.0: Ac 14 / Re 15. The 200-unit sample is 4.0% of the 5,000-unit lot.
How to Interpret AQL Results
Read the output as an acceptance-sampling plan, not as a measurement of the lot’s true defect rate. The sample size tells you how many units the plan calls for; Ac and Re tell you how the counted inspection results compare with that plan.
Ac and Re are decision thresholds
An Ac 10 / Re 11 plan means a count of 10 or fewer satisfies that sampling criterion, while a count of 11 or more reaches the rejection threshold. Apply the threshold only to the defect class and sample plan from which it was obtained.
The largest sample is not always the only plan
The calculator shows the largest resolved sample as the primary inspection quantity. If different AQLs resolve to different samples, the result details identify that condition because the Ac/Re pair belongs to its own resolved sample plan.
Passing does not prove the lot is below the AQL
Acceptance sampling is probabilistic. An accepted sample does not establish the exact percent nonconforming in the full lot, and a rejected sample does not by itself identify the process cause.