Which sampling method fits your QC mix?
In quality control (QC), one of the most important choices you make is not just what to inspect – but how much. Should you check every unit? A sample? And if so, how big should that sample be?
There’s no one-size-fits-all answer. But understanding the strengths, trade-offs, and use cases of different sampling methods can help you make the right decision based on your product, production setup, and risk profile.
Let’s break down the main approaches used in QC today.
100% Inspection: The all-in approach
As the name implies, 100% inspection means every single unit in a batch is checked. It’s the most thorough approach and often seen as the safest. Normally, all defects will be subject to rework using this approach.
When it’s used:
This method is commonly applied for high-end products where the value of a single piece is high enough to warrant the extra time spent. It can also be a good option for first-time production runs or when working with a new supplier.
Pros & cons:
While it offers maximum confidence, the cost and time investments are high. It’s also not immune to human error especially if inspections are rushed or repetitive. That’s why many companies use 100% checks selectively, based on risk and criticality.
AQL Sampling: A balance between risk and efficiency
AQL (Acceptable Quality Limit) is the most widely used sampling method in global supply chains. It uses statistical models to determine how many units to inspect and how many defects are acceptable based on predefined risk levels.
When it’s used:
AQL is especially useful when you need a repeatable, defensible way to evaluate quality without inspecting everything. It also serves the role as a common standard that both suppliers and customers can agree upon, which can somewhat reduce the need to discuss if a shipment has acceptable quality or not.
Pros & cons:
Choosing the right AQL level and understanding your defect categories (critical, major, minor) takes a little upfront work, but the payoff is a method that balances efficiency with confidence. For most mid-to-high-volume production runs, it strikes the best compromise between effort and insight.
Want to learn more about AQL, read our full guide here.
Percentage-based sampling: A simple approach
Percentage-based sampling is not widely used. Its main advantage is that it can be easier to understand than AQL, especially if you do not have a digital tool like Qarma to support AQL calculations. But it works poorly when shipment quantities change, and it also does not set any thresholds for acceptable quality.
How to choose the right method?
For high-end products, 100% inspection can be the right choice. For everything else, AQL is the recommended method.
There are many variations over AQL, so you need to define the appropriate sampling level and acceptable defect thresholds. For high-risk inspections, you can use Level III, whereas low-risk inspections can use level II or I. This will result in a balance between time spent on the inspection versus scrutiny and confidence in the results.
With our QC tool at Qarma, it’s easy to apply the right sampling method for each product and supplier. You simply select the method, assign the right checklist, and allocate the inspection to your team – all in one tool.
Keep in mind that your sampling methods is part of your overall QC mix – alongside clear quality standards, the right skills and training, a balanced inspection mix, and continuous feedback. Explore the QC mix here.
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