DEFINITION OF AQL AND DIFFERENT KINDS OF LEVEL

Definition of AQL: The AQL (Acceptable Quality Level) is the maximum per cent defective that for the purpose of sampling inspection can be considered satisfactory as a process average. 

Table: Sampling plan for shipment inspection:

Lot or Batch size	Sample size Code Letter	Sample Size	Acceptable Quality level
			2.5		4.0		6.5
			Ac	Re	Ac	Re	Ac	Re
2 – 8	A	2	0	1	0	1	0	1
9 – 15	B	3	0	1	0	1	0	1
15 – 25	C	5	0	1	0	1	0	1
26 – 50	D	8	0	1	1	2	1	2
51-90	E	13	1	2	1	2	2	3
91-150	F	20	1	2	2	3	3	4
151-280	G	32	2	3	3	4	5	6
251-500	H	50	3	4	5	6	7	8
501-1200	J	80	5	6	7	8	10	11
1201-3200	K	125	7	8	10	11	14	15
3201-10000	L	200	10	11	14	15	21	22
10001-35000	M	315	14	15	21	22	21	22
Source: ANSI/ASQ Z 1.4 The Sampling procedures and table for inspection by attributes

How to Read AQL table?

Lot or Batch size: This means total how many pieces inspector is going to check or inspect. (i.e. if you have been offered a shipment of 600 pieces order quantity, the batch size of this shipment will fall under 501 to 1200 pieces (Code-J)

Sample size Code letter: This code is indicative a range of batch size. (Code 'G' means your lot size range is from 151 pieces to 280 pieces.

Sample size: It means that how many pieces will be picked up for inspection from the total offered pieces (Batch).

Ac (Accepted): The number in this column denotes that if the inspector finds up to that much defective pieces the shipment will be accepted by buyer.

Re (Rejected): On the other hand number in this column denotes that if the inspector finds that much defective pieces or more than the listed number, the shipment will be rejected (or asked to the manufacturer for 100% inspection and re-offer for final inspection) by buyer.

Example: Suppose you have been offered a shipment of 1000 pieces for inspection. Select the range from table, it is 501-1200. Now from table you have to select number of sample you are going to actually inspect. According the above table you will select 80 pieces out of 1000 pieces. Now assume that you are inspecting at 2.5 AQL. So, after inspecting all 80 pieces if you find 5 or less than 5 defective pieces will accept the shipment. And if you find 6 or more than 6 defective pieces in 80 samples you will reject that shipment.