How to Calculate Sample Size in Garment Lot Inspection

Ever wondered how quality control teams decide whether a batch of 10,000 t-shirts is ready for retail shelves? They don’t check every single shirt—that would take forever and cost a fortune. Instead, the apparel industry relies on a precise, standardized methodology to pull just the right number of samples. This is called sample size for the inspection of an order or a production lot.

Whether you are launching your first apparel line or scaling up factory quality checks, mastering AQL (Acceptable Quality Limit) inspection standards—governed by ISO 2859-1 / ANSI/ASQ Z1.4—is essential to ensuring top-tier craftsmanship.

Here is a simple, step-by-step guide to calculating garment sample sizes like a pro.

Step 1: Count Your Total Lot Size

Start with the total quantity of finished units in the specific shipment or production run. For instance, let’s say your factory just completed a batch of 5,000 polo shirts.

Step 2: Select Your Inspection Level

Inspection severity dictates how thoroughly you sample a shipment. International standards define three general levels:

• Level II (General Default): The standard benchmark used across 90%+ of global garment quality checks.
• Level I (Reduced Inspection): Used for lower budgets, time-sensitive shipments, or factories with proven track records.
• Level III (Tightened Inspection): Used for high-end luxury garments, complex builds, or high-risk suppliers.

Step 3: Find Your Code Letter

Using the international standard Sample Size Code Letter Table, cross-reference your Lot Size against your Inspection Level (AQL Inspection):

Table-1: Code Letter based on Lot Size and General Inspection Level

Lot Size (Garments)	General Level I	General Level II (Standard)	General Level III
151 to 280	F	G	H
501 to 1,200	H	J	K
1,201 to 3,200	J	K	L
3,201 to 10,000	K	L	M
10,001 to 35,000	L	M	N

Step 4: Determine Your Sample Size & Pass/Fail Thresholds

Once you have your code letter, match it on the AQL Sampling Table to determine your exact sample size. Then, compare your findings against industry-standard defect limits:

• AQL 0: Critical Defects (e.g., exposed needles, broken sharp metal) –> Zero tolerance.
• AQL 2.5: Major Defects (e.g., incorrect sizing, open seams, prominent stains).
• AQL 4.0: Minor Defects (e.g., loose threads, minor print placement errors).

Table-2: Showing Code letter, Sample Size and Pass/Fail Defective unit in different AQL level

Code Letter	Sample Size to Inspect	AQL 1.0 (Strict) Pass / Fail	AQL 2.5 (Industry Std – Major)	AQL 4.0 (Minor)
G	32 pcs	Pass = 0 | Fail >=1	Pass <= 2 | Fail > =3	Pass <= 3 | Fail >= 4
J	80 pcs	Pass <= 2 | Fail >= 3	Pass <= 5 | Fail >= 6	Pass <= 7 | Fail >= 8
K	125 pcs	Pass <= 3 | Fail >= 4	Pass <= 7 | Fail >= 8	Pass <= 10 | Fail >=11
L	200 pcs	Pass <= 5 | Fail >= 6	Pass <= 10 | Fail >= 11	Pass <= 14 | Fail >= 15
M	315 pcs	Pass <= 7 | Fail >= 8	Pass <= 14 | Fail >= 15	Pass <= 21 | Fail >= 22

Example of Sample Size Calculation

Let’s look at a real-world scenario in the following example:

1. Total Order: 5,000 t-shirts (lot size) and inspection to be done full order in a single inspection.
2. Inspection Standard: Level II Standard. Chose you inspection level from options (Level I, II, III).
3. Code Letter: Matches to Letter L.
4. Action: Pull 200 garments at random across different cartons.
5. Verdict: At AQL 2.5, if you find 10 or fewer major defects, the shipment passes. If inspectors find 11 or more, the entire lot is rejected for factory re-work.

By implementing this systematic sampling approach, you can maintain consistency, manage supplier accountability, and keep your customers happy.

Sample Size Calculation (Calculator)