Determine the correct sample size and accept/reject numbers for your quality control inspection using the industry-standard AQL tables (ISO 2859-1 / ANSI Z1.4). Enter your lot size below to get instant results.
The Acceptable Quality Limit (AQL) is the cornerstone of modern quality control inspection. Defined by the international standard ISO 2859-1 (also known as ANSI/ASQ Z1.4 in the United States), AQL provides a statistically rigorous framework for deciding whether a production lot meets acceptable quality standards — without needing to inspect every single unit.
In international trade, AQL is used by importers, retailers, brands, and third-party inspection companies to make objective, data-driven accept/reject decisions on manufactured goods. Whether you are sourcing electronics from China, textiles from Bangladesh, or furniture from Vietnam, AQL sampling is the standard method used during pre-shipment inspections to evaluate product quality before shipment.
AQL works by defining three key parameters: the lot size (total number of units produced), the inspection level (which determines how rigorously you want to inspect), and the AQL percentage (the maximum acceptable defect rate). Together, these inputs determine exactly how many units to randomly select for inspection (the sample size) and how many defective units can be found before the lot is rejected.
The process relies on two lookup tables from ISO 2859-1. Table A maps your lot size and inspection level to a code letter (A through R). Table B then maps that code letter to the specific sample size and the accept/reject numbers for your chosen AQL value. If the number of defects found in your sample is equal to or below the accept number, the lot passes. If it equals or exceeds the reject number, the lot fails.
For businesses importing goods from overseas manufacturers, AQL provides an objective, internationally recognized standard for evaluating quality. Without AQL, quality decisions become subjective — leading to disputes between buyers and suppliers. With AQL, both parties agree in advance on the acceptable defect rate, creating clear expectations and a transparent inspection process.
AQL sampling is also far more practical than 100% inspection for large production runs. Inspecting every unit in a lot of 10,000 products would be prohibitively expensive and time-consuming. AQL sampling achieves statistically comparable confidence with a fraction of the units inspected — typically between 80 and 315 units for common lot sizes — saving significant time and cost while still protecting the buyer from shipping defective goods.
In practice, defects are classified into three categories, each with a different AQL threshold:
By applying different AQL thresholds to each defect category, inspectors can enforce strict standards for safety-critical issues while allowing reasonable tolerance for minor cosmetic variations. This three-tier approach is used by major retailers worldwide, including Walmart, Amazon, and Target, and is the standard methodology employed by professional quality control companies like Tetra Inspection.
The following tables are based on ISO 2859-1 / ANSI Z1.4 single sampling plans for normal inspection. Use Table A to find your sample size code letter, then Table B to determine the sample size and accept/reject numbers.
| Lot Size | Special Levels | General Levels | |||||
|---|---|---|---|---|---|---|---|
| S-1 | S-2 | S-3 | S-4 | I | II | III | |
| 2–8 | A | A | A | A | A | A | B |
| 9–15 | A | A | A | A | A | B | C |
| 16–25 | A | A | B | B | B | C | D |
| 26–50 | A | B | B | C | C | D | E |
| 51–90 | B | B | C | C | C | E | F |
| 91–150 | B | B | C | D | D | F | G |
| 151–280 | B | C | D | E | E | G | H |
| 281–500 | B | C | D | E | F | H | J |
| 501–1,200 | C | C | E | F | G | J | K |
| 1,201–3,200 | C | D | E | G | H | K | L |
| 3,201–10,000 | C | D | F | G | J | L | M |
| 10,001–35,000 | C | D | F | H | K | M | N |
| 35,001–150,000 | D | E | G | J | L | N | P |
| 150,001–500,000 | D | E | G | J | M | P | Q |
| 500,001+ | D | E | H | K | N | Q | R |
Level II (highlighted) is the default for most consumer product inspections.
| Code | Sample Size | 0.065 | 0.10 | 0.15 | 0.25 | 0.40 | 0.65 | 1.0 | 1.5 | 2.5 | 4.0 | 6.5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | Ac Re | ||
| A | 2 | — | — | — | — | — | — | — | — | 0 1 | 0 1 | 1 2 |
| B | 3 | — | — | — | — | — | — | — | 0 1 | 0 1 | 0 1 | 1 2 |
| C | 5 | — | — | — | — | — | — | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 |
| D | 8 | — | — | — | — | — | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 |
| E | 13 | — | — | — | — | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 |
| F | 20 | — | — | — | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 |
| G | 32 | — | — | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 |
| H | 50 | — | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 |
| J | 80 | 0 1 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 |
| K | 125 | 0 1 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 | — |
| L | 200 | 0 1 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 | — | — |
| M | 315 | 1 2 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 | — | — | — |
| N | 500 | 2 3 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 | — | — | — | — |
| P | 800 | 3 4 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 | — | — | — | — | — |
| Q | 1250 | 5 6 | 7 8 | 10 11 | 14 15 | 21 22 | — | — | — | — | — | — |
| R | 2000 | 7 8 | 10 11 | 14 15 | 21 22 | — | — | — | — | — | — | — |
AQL 2.5 column (highlighted) is the industry standard for major defects. “—” indicates the plan is not available for that combination; use the next available code letter.
Count or obtain the total number of units in the production lot you want to inspect. This is the total quantity produced, not the quantity you will inspect.
Choose an inspection level. General Inspection Level II is the default for most consumer products. Use Level I for lower-risk items or when cost savings are needed, and Level III for higher-risk or safety-critical products.
Using Table A (Sample Size Code Letters), find the row matching your lot size range, then read across to your chosen inspection level to find the code letter (A through R).
Select the AQL percentage for each defect category: typically 0.0–0.65% for critical defects, 1.0–2.5% for major defects, and 2.5–4.0% for minor defects. AQL 2.5 is the industry standard for general consumer goods.
Using Table B (Single Sampling Plans for Normal Inspection), find the row for your code letter. Read across to your AQL value to find the accept number (Ac) and reject number (Re). The sample size is shown in the second column.
Randomly select the specified number of units from the lot and inspect each one. Count the total defects found. If defects are equal to or less than the Accept number, the lot passes. If defects are equal to or greater than the Reject number, the lot fails.
You have a lot of 4,000 units and want to use General Inspection Level II with AQL 2.5 for major defects. From Table A, a lot size of 3,201–10,000 at Level II gives code letter L. From Table B, code letter L has a sample size of 200 units, with Accept = 21 and Reject = 22. You randomly select 200 units, inspect them, and count defects. If you find 21 or fewer major defects, the lot passes. If you find 22 or more, the lot fails.
AQL (Acceptable Quality Limit) is the worst tolerable quality level for a production lot during random sampling inspection. Defined in ISO 2859-1 and ANSI/ASQ Z1.4, it tells you how many units to inspect from a batch and the maximum defects allowed before rejecting the entire lot.
The standard defines three General Inspection Levels (I, II, III) and four Special Levels (S-1 through S-4). Level II is the default for most consumer products. Higher levels mean larger sample sizes and greater confidence, while special levels are used for destructive or expensive testing.
0.0 – 0.65% — Critical defects (safety hazards, regulatory non-compliance)
1.0 – 2.5% — Major defects (product does not function as intended)
2.5 – 4.0% — Minor defects (cosmetic issues that do not affect function)
A sampling plan specifies the sample size (number of units to inspect) and the accept/reject criteria. The standard provides plans for single, double, and multiple sampling. Our calculator uses single sampling plans — the most commonly used method in international trade.
ISO 2859-1 defines switching rules between normal, tightened, and reduced inspection. Start with normal inspection. Switch to tightened if 2 of 5 consecutive lots are rejected. Switch to reduced if 5 consecutive lots pass and production is stable. Return to normal if a lot is rejected under reduced inspection.
AQL sampling is faster and more cost-effective than 100% inspection while still providing high statistical confidence. It is the global industry standard used by importers, retailers, and quality control firms like Tetra Inspection to make objective accept/reject decisions on production lots.
AQL stands for Acceptable Quality Limit. It is a statistical method defined in ISO 2859-1 (ANSI/ASQ Z1.4) used to determine how many units from a production lot should be randomly inspected and the maximum number of defective units allowed before the lot is rejected. AQL is the industry standard for quality control inspections worldwide.
AQL 2.5 means the acceptable quality limit is set at 2.5%. This is the most commonly used AQL value for general consumer products and is the industry standard for major defects in pre-shipment inspections. With AQL 2.5, a lot is statistically expected to contain no more than 2.5% defective units. It strikes a balance between quality assurance and practical inspection costs.
The most commonly used AQL levels are: 0.0–0.65% for critical defects (safety hazards), 1.0–2.5% for major defects (functional issues), and 2.5–4.0% for minor defects (cosmetic imperfections). An AQL of 2.5 is the industry default for general consumer products. Stricter AQL values (lower numbers) mean tighter quality requirements and larger sample sizes.
General Inspection Level II is the default and most widely used level. Level I requires fewer samples (less discrimination) and is used when lower inspection costs are needed or the process is well-established. Level III requires more samples (higher discrimination) and is used when stricter quality assurance is required, such as for safety-critical products. The higher the level, the larger the sample size and the greater the statistical confidence in the result.
After inspecting the specified sample size, count the total number of defective units found. If the count is equal to or less than the Accept number (Ac), the lot passes inspection. If the count is equal to or greater than the Reject number (Re), the lot fails. For example, with Ac = 3 and Re = 4, finding 3 or fewer defects means the lot is accepted; 4 or more means it is rejected.
Normal inspection is the default starting level. Tightened inspection is switched to when 2 out of 5 consecutive lots have been rejected — it uses stricter accept/reject numbers. Reduced inspection is used when 5 consecutive lots have been accepted under normal inspection and production is stable — it allows smaller sample sizes to save costs. These switching rules are defined in ISO 2859-1.
No. AQL is a statistical sampling method where only a randomly selected portion of the lot is inspected. It provides a high confidence level that the lot meets quality requirements without inspecting every unit. 100% inspection checks every single unit and is typically reserved for critical safety items or very small lot sizes. AQL sampling is far more cost-effective for large production runs.
Special Inspection Levels (S-1, S-2, S-3, S-4) are used when very small sample sizes are needed, typically for destructive testing where inspected units cannot be sold, or for expensive products where minimizing sample size is important. S-1 uses the smallest sample and S-4 the largest among special levels. These levels provide lower statistical discrimination than general levels but are appropriate when testing is costly or destructive.
Let Tetra Inspection handle your AQL sampling on-site. We provide third-party quality control inspections in 45+ countries.
