Guide
Sample requirements: how many, what size?
The sample is the most overlooked yet most result-defining part of a test. A wrongly taken or insufficiently submitted sample invalidates even a correctly performed test.
The method standard determines how many samples and what size are required; the same product requires different samples under different standards. This page does not give an exact quantity — it explains the factors that determine the number and the shipping rules. The exact quantity is communicated at the quote stage based on the test's standard.
What does it depend on?
What determines the sample quantity and size?
Method standard
Each test method defines its own sample geometry and minimum quantity. In a tensile test the sample is machined, in an impact test a notch is cut; the two may not be obtainable from the same part.
Statistical evaluation
If the result is reported as a mean and distribution, a single sample is not enough. For defect-sensitive materials (ceramics, composites), the sample count increases significantly to obtain a meaningful distribution.
Whether it is destructive
If the sample is destroyed during the test, a separate sample is required for each condition. Vibration on three axes may mean three separate samples; this should be agreed in the test plan in advance.
Conditioning and spares
Keeping spares for samples damaged during conditioning or affected by measurement error is cheaper than replanning the test from scratch.
Direction and location
In rolled, woven or injection-moulded materials, properties vary by direction. It must be stated in which direction and from where in the product the sample was taken.
Retained/witness sample
For work with a potential for dispute, it is recommended to set aside a second set from the same batch. A retained sample allows for retesting if the result is disputed.
Shipping rules
The following apply to every sample regardless of product group.
- LabellingEvery sample must bear the product name, batch/lot number, and a direction mark if applicable. An unlabelled sample is not accepted at the laboratory.
- PackagingThe sample must be packaged so it is not damaged during transport. Surfaces to be tested must not be scratched, and in corrosion tests the surface must not be touched by hand.
- Cold chainFor food, cosmetic and biological samples, the chain must not be broken. If temperature recording is required, a data logger must be included with the shipment.
- Safety data sheetFor samples containing chemicals, a safety data sheet (SDS) must be sent together with the sample; transport and in-lab handling are planned accordingly.
- Document attachmentThe product description, the standard to be applied, the requested test, and any customer specification must be sent together with the sample. Missing information delays the start of the test.
- Return preferenceFor non-destructive tests, whether the sample will be returned must be stated at the outset; otherwise the sample is destroyed at the end of the retention period.
Points to note by product group
Metal and mechanical tests
- The sample must be taken with knowledge of the product's rolling or casting direction.
- For welded samples, the position of the seam within the sample must be stated.
- The heat treatment condition (temper, normalization) must be stated.
- Heating during cutting can alter the material structure; cooled cutting should be preferred.
Plastics and composites
- Samples should preferably be taken from the same mould and the same production settings.
- The injection flow direction is decisive for the result; it must be stated.
- The pre-test conditioning time is often longer than the test itself and must be included in planning.
- For moisture-absorbing polymers, the sample must be sent in sealed packaging.
Electrical, electronic and EMC
- The product must be sent in its series production configuration, with all accessories and cables.
- Cable types and lengths must reflect the actual installation.
- The functional check procedure and pass criteria must be provided in writing.
- The software version must be recorded and not changed during the test.
Food and microbiology
- The sample must be sent in its original, unopened packaging.
- Aseptic sampling rules must be followed, and the container must be sterile.
- The production and best-before dates along with batch information must be stated.
- For products requiring cold chain, the chain must not be broken.
Cosmetics
- The product must be sent in the packaging in which it will be offered for sale.
- The ingredients list (INCI) must be shared.
- A sufficient number of samples from the same batch must be set aside for the stability study.
- Light-sensitive products must be transported in dark packaging.
Construction materials
- The sample must be taken in a way that represents the batch and in accordance with the standard's sampling rules.
- The date, location and person who took the sample must be recorded.
- Samples requiring curing must be stored under defined conditions and delivered on time.
- No cracks or edge chips must occur in the sample during transport.
Frequently asked questions
- How do I find out how many samples I need to send?
- The exact quantity is specified in the applicable method standard and is communicated together with the test plan at the quote stage. A number given without knowing the standard is misleading.
- What happens if the sample sent is insufficient?
- The test is not started and the missing quantity is reported. A test performed with an insufficient sample is not considered compliant with the standard; the result cannot be reported.
- Will my sample be returned?
- Return is possible for non-destructive tests, and this preference must be stated at the outset. In destructive tests the sample is destroyed during the test.
- How long are samples retained?
- The retention period is determined by the type of test and the laboratory's quality system; at the end of the period the sample is destroyed. If longer retention is desired, it must be stated in writing in advance.
To learn the exact sample quantity and size your test requires, simply state the product and the standard to be applied in your quote request.
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