Short answer: Nominal diameter is the product’s stated size category; a certified or characterized diameter is a measurement result produced by a defined method with associated uncertainty and documentation. Buyers should not assume that every “100 nm” standard has the same certified value, method or uncertainty.
Decision rule: Specify the measurement purpose and required documentation—not only the nominal size printed in the catalog.
Nominal size is a selection label
Nominal size helps buyers choose the approximate standard. It may be based on a target manufacturing size or rounded characterization result. It is not automatically the value that should be entered into a calibration method.
Certified or characterized values depend on the method
Particle diameter can be evaluated using different physical measurement principles. Each method has its own measurand, sample preparation and uncertainty contributors. A certificate should identify the value, method, conditions and uncertainty or other characterization statement relevant to the product.
Distribution width matters
A mean diameter alone does not describe the particle population. Monodispersity, standard deviation, coefficient of variation or distribution data can be important when the instrument response depends on a narrow size population.
Refractive response can matter to optical instruments
Optical particle instruments respond to light scattering, which depends on more than physical diameter. Particle material and refractive properties can influence the instrument response. Use the material and assigned value required by the method rather than substituting solely by nominal diameter.
Write the purchase specification
| Field | Example requirement |
|---|---|
| Nominal size | Approximate target used to select the product |
| Assigned value | Certified or characterized value required by the method |
| Material | PSL, silica or other specified composition |
| Distribution | Required uniformity or distribution information |
| Documentation | Certificate type, method, uncertainty and traceability statement |
Working checklist
- Instrument and method
- Nominal size
- Required assigned value
- Particle material
- Distribution requirement
- Concentration or loading
- Certificate and uncertainty requirement
- Storage and expiration controls
What to include in the RFQ
Provide the instrument, method, nominal size, required assigned-value documentation, material, presentation format and quantity.
Use the GSE technical RFQ to submit the requirement, attachments, destination and required-on-site date.
Read the certificate as part of the product
The label’s nominal diameter is a convenient product designation. The certificate should identify the assigned value, measurement method, uncertainty or tolerance statement, lot identity and traceability basis. Buyers should verify which value their instrument procedure requires and whether the certificate format contains the fields their quality system expects.
A nominal match alone is not enough when the instrument method specifies a certified size window. Put the acceptable assigned-value range and documentation requirements into the purchase order so substitutions are evaluated before shipment.
Continue the topic: Particle Metrology Knowledge Center.
Authoritative references
This guide translates public requirements and technical concepts into purchasing and study-planning questions. The controlling standard, regulation, site procedure and quality approval remain authoritative.
Frequently asked questions
Is nominal diameter the same as certified diameter?
No. Nominal diameter is a product designation; the certificate or characterization report provides the measured value and method.
Why can different methods report different values?
They may measure different physical aspects of the particle and have different sample-preparation and uncertainty contributions.
Should uncertainty be part of the purchase requirement?
Yes, when the calibration or validation method depends on a stated measurement uncertainty.
Turn this research into a controlled technical request.
Send the application, model, specification or drawing. GSE will preserve the technical lane, identify missing scope and verify current commercial details without treating website copy as an offer.
- Unique request reference
- Completeness score
- Technical-lane routing
- No fabricated channel or inventory claims