How to determine the correct Quantity levels for Inspections

How to determine the correct quantity and acceptable fault levels when inspecting a product

How to determine the quantity to be inspected

While we all would like to have every single unit of goods to be inspected, this is simply not practicable or affordable for most products and companies.

The best approach, which is recommended by International Standards Agencies such as ANSI/ ASQ, is to use the AQL (Acceptable Quality Limit or Level) approach to determine both the sample inspection size and the levels required to determine of an Inspection is a Pass or a Fail.

We use the internationally recognized Acceptable Quality Limit (AQL) standard for all product inspections. For each inspection, this allows the client to set their acceptable quality tolerance levels.

What is AQL (Acceptable Quality Limit or Level)?

AQL is sometimes called Acceptable Quality Limit by some people or Acceptable Quality Level by others. They both essentially mean the same thing.

To determine the AQL level of a product you need to use the measure table that is recommended by ISO 2859, NF06-022, DIN 40080, BS 6001, ANSI/ASQC Z1.4.

This table allows you to determine the sample size (amount or quantity) that should be taken from an order or batch to be inspected or tested. It then provides you with the values to determine whether a product has met the buyers specifications and passes or fails the inspection.

You can then determine the tolerance levels in terms of Critical, Major and Minor levels for your product. The tolerance levels is a fair and equitable method which gives the seller and the buyer leeway to determine what is an Pass or Fail for an order.

The way to determine these are below:

Critical defects (totally unacceptable: a user might get harmed, or regulations are not respected) – 0% e.g. plug on an electrical device and it smokes, or a non-welded bar in a bed The product is dangerous
Major defects (these products would usually not be considered acceptable by the end user) – usually 2.5% e.g. scratches that are noticeable and may prevent the product being sold
Minor defects (there is some departure from specifications, but most users would not mind it). – usually 4.0% e.g. a small scratch on the bottom of a leg of a bed, or on non-visual piece on an electrical appliance

All Inspection reports generated by the inspection companies listed on Goodada.com will clearly display the AQL standards and show you if the production has failed or passed.

How do I calculate the correct sample size and acceptance value?

For the majority of products the best suggestion is to use a Standard Level II. If this is the accepted Level then the table below will provide the sample size, critical, major and minor vales (acceptable value) see the page below

Lot Size	Sample Size	Critical Defects	Major Defects	Minor Defects
2-8	2	0	≤ 0	≤ 0
9-15	3	0	≤ 0	≤ 0
16-25	5	0	≤ 0	≤ 0
26-50	8	0	≤ 0	≤ 1
51-90	13	0	≤ 1	≤ 1
91-150	20	0	≤ 1	≤ 2
151-280	32	0	≤ 2	≤ 3
281-500	50	0	≤ 3	≤ 5
501-1200	80	0	≤ 5	≤ 7
1201-3200	125	0	≤ 7	≤ 10
3201-10000	200	0	≤ 10	≤ 14
10001-35000	315	0	≤ 14	≤ 21
35001-150000	500	0	≤ 21	≤ 21
150001-500000	800	0	≤ 21	≤ 21
500000 and over	1250	0	≤ 21	≤ 21

For any non-standard products, or products where the buyer requires a more detailed inspection, please refer to the tables below.

Our inspectors would be delighted to assist you to determine the correct levels, sample size and acceptance numbers

Sample Size Chart – this will allow you to determine the amount or quantity of your sample

Lot Size	General Inspection Levels			Specific Inspection Levels
	I	II	III	S-1	S-2	S-3	S-4
2-8	A	A	B	A	A	A	A
9-15	A	B	C	A	A	A	A
16-25	B	C	D	A	A	B	B
26-50	C	D	E	A	B	B	C
51-90	C	E	F	B	B	C	C
91-150	D	F	G	B	B	C	D
151-280	E	G	H	B	C	D	E
281-500	F	H	J	B	C	D	E
501-1200	G	J	K	C	C	E	F
1201-3200	H	K	L	C	D	E	G
3201-10000	J	L	M	C	D	F	G
10001-35000	K	M	N	C	D	F	H
35001-150000	L	N	P	D	E	G	J
150001-500000	M	P	Q	D	E	G	J
500000 and over	N	Q	R	D	E	H	K

Use the letter identified in the Sample Size Chart to determine the Acceptance Values and Sample Size

Code Letter	Sample Size			Standard Major	Standard Minor
Code Letter	Sample Size	1.0%	1.5%	2.5%	4.0%	6.5%
A	2	≤ 0	≤ 0	≤ 0	≤ 0	≤ 0
B	3	≤ 0	≤ 0	≤ 0	≤ 0	≤ 0
C	5	≤ 0	≤ 0	≤ 0	≤ 0	≤ 1
D	8	≤ 0	≤ 0	≤ 0	≤ 1	≤ 1
E	13	≤ 0	≤ 0	≤ 1	≤ 1	≤ 2
F	20	≤ 0	≤ 1	≤ 1	≤ 2	≤ 3
G	32	≤ 1	≤ 1	≤ 2	≤ 3	≤ 5
H	50	≤ 1	≤ 2	≤ 3	≤ 5	≤ 7
J	80	≤ 2	≤ 3	≤ 5	≤ 7	≤ 10
K	125	≤ 3	≤ 5	≤ 7	≤ 10	≤ 14
L	200	≤ 5	≤ 7	≤ 10	≤ 14	≤ 21
M	315	≤ 7	≤ 10	≤ 14	≤ 21	≤ 21
N	500	≤ 10	≤ 14	≤ 21	≤ 21	≤ 21
P	800	≤ 14	≤ 21	≤ 21	≤ 21	≤ 21
Q	1250	≤ 21	≤ 21	≤ 21	≤ 21	≤ 21
R	2000	≤ 21	≤ 21	≤ 21	≤ 21	≤ 21

13 Comments

Md. Monzurul Islam
December 13, 2017 at 6:05 am | Permalink

How much will the sample quantity if a lot/batch of 10000 piece consists of 5000 red & 50000 black garments

- admin
  July 20, 2018 at 11:04 am | Permalink
  
  Hi,
  You would need to look at 200 red and 200 black
  
Eric Brachhausen
June 24, 2018 at 5:48 pm | Permalink

Very good article, and thank you for posting it. Question: Suppose an order of 100 boxes of parts arrives, and each box contains 50 parts. The nature of the inspection is general, level II. What is the appropriate lot size? Would it be 100, 50, or some other number?

- admin
  July 20, 2018 at 11:03 am | Permalink
  
  Its broken down into the individual groups of parts
  
kay
August 16, 2018 at 2:41 pm | Permalink

Good Article. Check for HDPE from bulk truck to silo bulk truck 40,000# – how much do I need to test ?

- admin
  August 22, 2018 at 10:47 am | Permalink
  
  Hi Kay,
  You should discuss with your QA department.
  You can look at breaking the total volume down into smaller units say 20kg and then proceed to determine how much to be tested.
  
  But I do suggest that you speak with your QA department and get their confirmation.
  
Martina
August 22, 2018 at 3:39 pm | Permalink

Hi, I have a batch of 1700 pieces, I have checked 200 pieces and 10 from these have MAJOR defects.. do I need to check the whole batch or can I reject the batch and send it back to supplier? Thank you

Rich
September 20, 2018 at 5:43 pm | Permalink

So is the AQL based on the smallest unit of measure? If I have 1 case containing 25 packs, with 10 units in each pack. Is my sample size 250 or 1 case. The inspection level is II, AQL level is 0.65.

Prashanth
September 24, 2018 at 12:50 pm | Permalink

Very informative. Thanks.
Hi Eric. As per my understanding the lot size will neither be 100 nor 50. Since the total num of parts is 100*50=5000, the lot size would be 200.

David Schaefer
February 28, 2019 at 5:05 pm | Permalink

Real World nasty little question here… Lets say you have a predetermined sample size you can test, regardless of the Lot size. How can you work backwards to calculate the best possible AQL? Please note, the available sample size is less than what is prescribed by the charts. Thanks for your help!

CM
March 10, 2019 at 11:03 pm | Permalink

Hi,
If I have a lot size of 250 pcs. Under level II, I should check 32 pcs. The AQL level is minor 4 and major 2.5.
Scenario 1 – if I find 3 pcs with minor defect and 1pc of major defect… the lot accepted?
Scenario 2 – if I find 4 pcs minor defect, the lot should be rejected.
If the above scenario is correct, I have a doubt that if I classify scenario 1 critical defect as minor defect, then the lot will be rejected, right?

Simon B
March 18, 2019 at 10:53 am | Permalink

Hi, is it possible to apply similar quality acceptability formulae to products where the “sample size” is 100%, i.e. customer complaints?

- Aidan Conaty
  March 22, 2019 at 10:09 am | Permalink
  
  Hi,
  You would need to apply your discretion in this instance.