SAP QM Sample Size Calculation: Lot Size, AQL, Percentage and Fixed Sample
In SAP QM the sample size of an inspection lot comes from the sampling procedure assigned to a characteristic or inspection type. This calculator shows what three common procedures give for the same lot, so you can pick the one that balances risk and effort.
Your numbers
Quantity in the inspection lot (QALS lot size).
General level II is the usual default. Level III draws a larger sample for the same lot size.
Used when the sampling procedure is a percentage of the lot.
Used when the sampling procedure is a fixed sample.
All characteristics for one sample unit.
Your results
The AQL-based figure follows the sample size code letter structure of ANSI/ASQ Z1.4 for single sampling, normal severity, general levels II and III. Acceptance and rejection numbers depend on the AQL you choose and are not calculated here. Your SAP sampling procedure and dynamic modification rule may differ, so use this as a planning check.
Sample size by lot size under each rule
Sweeps Inspection lot size from 50 to 20000, holding your other inputs fixed.
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How to use the calculator
Enter the lot size, pick an inspection level and set the percentage and fixed sample values you are considering. The three sample sizes appear side by side, and the chart shows how each rule scales with lot size. The AQL-based result grows slowly while the percentage rule grows linearly, which is why percentage sampling becomes expensive on large lots.
- Use the AQL result when you want risk based on a defined quality level.
- Use the fixed sample when lots vary but effort must stay constant.
- Use the percentage rule only when the process really needs proportional checks.
How SAP QM defines the sample
A sampling procedure in SAP defines how the sample size is found: all units, a fixed number, a percentage, or an AQL-based plan with a sampling scheme. The sampling scheme holds the table of lot size ranges and the acceptance numbers. A dynamic modification rule can move a vendor between normal, reduced, tightened and skip stages depending on past lot results. The inspection lot receives the final sample size when it is created.
Worked example
A lot of 2,500 pieces falls in the 1,201 to 3,200 band. At general level II the code letter is K and the table sample size is 125 pieces, about 5 percent of the lot. At level III it moves to L and 200 pieces. A 5 percent rule gives 125 as well, but at 10,000 pieces it would ask for 500 while the AQL table asks for 200. At 3 minutes per piece, 125 pieces needs about 6.3 hours.
Common mistakes
Common errors are treating the sample size as the only control, when acceptance numbers matter just as much, applying one sampling procedure to both attribute and variable characteristics, and forgetting that the lot may be smaller than the table sample, which means 100 percent inspection. Also check whether your dynamic modification rule is lowering the stage, since reduced stages use a smaller sample.
Frequently Asked Questions
How does SAP QM calculate sample size?
It reads the sampling procedure assigned to the characteristic or inspection setup. The procedure can inspect all units, a fixed sample, a percentage, or use an AQL plan from a sampling scheme by lot size. The result is stored on the inspection lot when it is created.
What is a sampling procedure in SAP QM?
It is a master data object that combines a sampling type, such as fixed, percentage or according to a sampling scheme, with a valuation mode. It can also point to a dynamic modification rule. You assign it in the inspection plan or in the master inspection characteristic.
What does dynamic modification do?
It changes the inspection stage by quality history. After a run of good lots the stage can go to reduced or skip, and after bad lots to tightened. The stage changes the effective sample size or whether a lot is inspected at all. It is set up in the dynamic modification rule.
What if the lot is smaller than the sample size?
Then the sample equals the lot, which means every piece is inspected. This calculator caps the result at the lot size to show that. In SAP the same applies, a sample can never exceed the inspected quantity of the lot.
If you want sampling rules, dynamic modification and inspection effort reviewed against your actual vendor history, we can help check your SAP QM setup. The calculator works on its own.
Related Tools
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Find the Z1.4 sample size code letter and single sampling sample size for a lot, then see how likely the lot is to be accepted at a given defect rate.
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Model how much inspection effort a skip or reduced stage saves, based on the share of lots that run at the reduced stage.
SAPSAP QM Zero Acceptance Sample Size Calculator
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SAPSAP QM OC Curve and Acceptance Probability Calculator
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