AQL stands for Acceptance Quality Level (or Limit). It is the maximum percentage of defective units in a lot that is considered acceptable as a process average. An AQL of 1.0% means lots averaging 1% defective will be accepted most of the time.

What inspection level should I use?

General Level II is the default and most commonly used. Level I uses smaller samples (less protection), Level III uses larger samples (more protection). Special levels S-1 to S-4 are for very small samples or destructive testing.

What happens when a lot is rejected?

Rejected lots may be 100% sorted (screening), returned to the supplier, reworked, or scrapped. The disposition depends on your quality agreement and the severity of defects found.

Is AQL sampling a guarantee of quality?

No. AQL sampling controls the long-run average quality of accepted lots. Individual lots with higher defect rates can be occasionally accepted (producer's risk) and good lots can be occasionally rejected (consumer's risk).

What is switching between normal, tightened, and reduced inspection?

Per Z1.4, you switch to tightened inspection after 2 of 5 lots are rejected, back to normal after 5 consecutive acceptances, and to reduced after 10 consecutive normal acceptances with low defect counts.

Can I use AQL for service quality?

Yes. AQL sampling can be applied to any countable population — invoices, transactions, data records, etc. Define a "unit" and a "defect" appropriately for your service context.

Sample Size AQL Calculator

Determine inspection sample size and accept/reject numbers based on ANSI/ASQ Z1.4 AQL tables. Plan incoming and in-process inspections.

Lot Size

AQL Level

Code Letter

General Level II

Sample Size

200

Units to inspect

Accept (Ac)

Accept if defects ≤ 5

Reject (Re)

Reject if defects ≥ 6

Planning notes, formulas, and examples

About the Sample Size AQL Calculator

Acceptance Quality Level (AQL) sampling determines how many units from a production lot must be inspected and how many defects are acceptable before the lot is accepted or rejected. The ANSI/ASQ Z1.4 standard (also known as MIL-STD-1916 successor and ISO 2859-1) provides standardized tables that map lot sizes and AQL levels to sample sizes and accept/reject numbers.

AQL sampling balances inspection cost against quality risk. Inspecting every unit (100% inspection) is expensive and often impractical. AQL plans provide statistically justified sample sizes that control the probability of incorrectly accepting bad lots or rejecting good lots.

This calculator takes your lot size, AQL level, and inspection level to determine the sample size and accept/reject criteria, simplifying the lookup process that quality inspectors traditionally perform with printed tables.

This measurement forms a critical foundation for capacity planning, helping teams align production capabilities with demand forecasts and strategic business objectives throughout the planning cycle.

When This Page Helps

AQL sampling provides a standardized, statistically sound method for lot acceptance that is recognized worldwide. It eliminates subjective sample size decisions and ensures consistent quality decisions across suppliers, inspectors, and facilities.

How to Use the Inputs

Determine the production lot size.
Select the desired AQL level (e.g., 0.65%, 1.0%, 2.5%).
Select the inspection level (General Level II is standard).
Enter these values into the calculator.
Review the sample size and accept/reject numbers.
Inspect the specified number of units and compare defects found against the accept number.

Formula used

Based on ANSI/ASQ Z1.4 tables:

1. Lot size → Sample size code letter (using inspection level table)
2. Code letter + AQL → Sample size (n), Accept number (Ac), Reject number (Re)

If defects found ≤ Ac → Accept lot
If defects found ≥ Re → Reject lot

Example Calculation

Result: Sample size = 200, Ac = 5, Re = 6

For a lot of 5,000 units at AQL 1.0% with General Inspection Level II, the code letter is L, giving a sample of 200 units. Accept the lot if 5 or fewer defects are found; reject if 6 or more.

Tips & Best Practices

General Level II is the default inspection level; use Level I for reduced and Level III for tightened inspection.
Switch to tightened inspection if 2 out of 5 consecutive lots are rejected.
Return to normal from tightened after 5 consecutive lots are accepted.
AQL applies to the process average, not to individual lot quality — it is a long-run metric.
For critical defects (safety), consider AQL = 0 and 100% inspection or special sampling plans.
Document your AQL plan in your quality manual and share it with suppliers.

Understanding AQL Tables

The Z1.4 tables are organized in two stages. First, a lot-size/inspection-level table converts your lot size and inspection level to a code letter (A through R). Second, a code-letter/AQL table converts the code letter and desired AQL to sample size (n), accept number (Ac), and reject number (Re).

When to Use 100% Inspection Instead

For critical safety defects, AQL sampling may not provide adequate protection. Consider 100% inspection (with adequate gage capability) for characteristics where even one defect poses serious risk to consumers or end users.

AQL in International Trade

AQL sampling is the international standard for import/export quality inspection. Third-party inspection companies use AQL plans to evaluate shipments on behalf of buyers, providing an objective quality gate at the point of manufacture.

Sources & Methodology

Last updated: February 9, 2026

Frequently Asked Questions

AQL stands for Acceptance Quality Level (or Limit). It is the maximum percentage of defective units in a lot that is considered acceptable as a process average. An AQL of 1.0% means lots averaging 1% defective will be accepted most of the time.