ANSI/ASQ Z1.4 Table

In international manufacturing, the ANSI/ASQ Z1.4 table is the industry-standard mathematical blueprint used to determine exactly how many products an inspector must check, and how many defects are allowed before a shipment is rejected.

For many global sourcing managers, looking at these technical charts for the first time can be overwhelming. This guide breaks down the ANSI/ASQ Z1.4 tables into a clear, actionable workflow, showing you exactly how third-party QC agencies calculate sampling sizes and pass/fail thresholds.

What is the ANSI/ASQ Z1.4 Table?

The ANSI/ASQ Z1.4 standard (originally derived from the military standard MIL-STD-105E) defines sampling procedures and tables for inspection by attributes. It functions as a two-part matrix:

1. Table 1 (Sample Size Code Letters): Cross-references your total order quantity with an inspection level to give you a single "Code Letter."
2. Table 2 (Single Sampling Plans for Normal Inspection): Cross-references that "Code Letter" with your chosen AQL percentage to give you the exact sample size and Ac / Re (Accept / Reject) limits.

Choosing Your Inspection Level: General vs. Special

Before opening the table, you must select an Inspection Level. Table 1 offers two main categories:

General Inspection Levels (Levels I, II, III)

These are used for non-destructive visual and functional checks.

• Level II: The universal industry standard. It offers a balanced compromise between inspection cost and statistical reliability.
• Level I: Fewer samples checked. Used when budget is highly restricted or supplier history is flawless.
• Level III: More samples checked. Used for high-value goods or when a supplier has a history of severe quality failures.

Special Inspection Levels (S-1, S-2, S-3, S-4)

These are reserved for destructive or time-consuming tests (e.g., battery drop tests, high-voltage checks, fabric tensile strength tests) where checking a large volume would destroy commercial inventory.

How to Read Table 1: Finding Your Code Letter

Let's use a real-world scenario: You are importing 5,000 units of wireless headphones, and you select General Inspection Level II.

1. Look at the Lot or Batch Size column on the left side of Table 1.
2. Find the range that includes your quantity. For 5,000 units, the correct row is 3,201 to 10,000.
3. Move horizontally across that row to the column for General Inspection Level II.
4. The intersection reveals your Sample Size Code Letter: K.

How to Read Table 2: Determining Sample Size and Ac/Re

Now that you have your Code Letter (K), switch to Table 2 (Single Sampling Plans for Normal Inspection).

Click to AQL Sampling Calculator

Step 1: Identify the Sample Size

Look up Letter K in the leftmost column. Directly next to it, the table indicates the mandatory Sample Size: 125. This means the inspector will randomly select exactly 125 headphones out of your total 5,000-unit batch.

Step 2: Cross-Reference with Your Chosen AQL

Assume your contract defines the quality standards as AQL 2.5 for Major Defects and AQL 4.0 for Minor Defects.

• For Major Defects (AQL 2.5): Follow the row for Letter K to the right until you align with the 2.5% column. You will find the numbers Ac: 7 and Re: 8.
• For Minor Defects (AQL 4.0): Follow the row to the 4.0% column. You will find the numbers Ac: 10 and Re: 11.

Scoring the Final QC Report: Pass or Fail?

During the on-site inspection, the inspector checks the 125 units and tallies the defects. Here is how to apply the chart's math to the final score:

Scenario A: The Batch Passes

The inspector finds 6 Major defects and 9 Minor defects.

• 6 Major is less than or equal to the Ac threshold of 7.
• 9 Minor is less than or equal to the Ac threshold of 10.
• Result: The production lot officially PASSES AQL standards, and you can authorize shipment.

Scenario B: The Batch Fails

The inspector finds 8 Major defects and 4 Minor defects.

• Even though Minor defects are well within the limit, the 8 Major defects hit the Re threshold of 8.
• Result: The production lot officially FAILS. You have the legal right to hold final payment and instruct the factory to re-sort and rework the cargo at their expense.