What's the Difference Between NIST and ISO/IEC 17025 Calibration?

The National Institute of Standards and Technology (NIST) is the U.S. National Metrology Institute responsible for maintaining primary measurement standards. ISO/IEC 17025 is the internationally recognized standard for testing and calibration laboratories. Both organizations provide widely recognized calibration frameworks used to ensure accurate, reliable measurement results across many industries.

Although these terms are often associated with pressure instruments, both NIST traceability and ISO/IEC 17025 accreditation apply to the calibration laboratories performing the work, not to the instruments themselves.

Selecting which calibration testing method is needed for pressure measurement depends on how the instrument will be used. As a trusted authority in pressure and temperature measurement, Ashcroft frequently guides customers who are seeking clarity on calibration standards, documentation requirements and best practices for testing and maintaining measurement accuracy.

Read this article to learn how NIST traceable and ISO/IEC 17025 accredited calibrations differ, what each certification means and how to determine the right level of calibration for your application.

What Is a NIST Traceable Calibration?

A NIST traceable calibration is a more cost-effective method that ensures the calibration standard is traceable to the U.S. National Measurement Institute. A NIST traceable calibration verifies:

• Reference standards used during calibration can be traced back to NIST through an unbroken chain of comparisons. This confirms your instrument aligns with U.S. national measurement standards, providing a reliable baseline for industrial measurements.
• Calibration documentation showing the traceability chain. This allows users to verify exactly how measurements were established, helping support internal quality processes and audits.
• Consistency with national measurement standards. This verifies pressure readings remain uniform across different locations or equipment using NIST-traceable references.

What a NIST traceable calibration does not include, and why it matters

• No assessment of laboratory competence. This provides faster and more affordable calibration services for applications that don’t require full lab accreditation.
• No validated method review. This is suitable for general-purpose or non-regulated processes where method verification is not required.
• No environmental condition verification. Helps streamline calibration for routine industrial measurements where control of temperature or vibration is not critical.
• No measurement uncertainty requirement. Provides fewer documentation requirements, which is ideal when uncertainty values are not required by the quality system.

NIST traceable calibration key Benefits: 

• Cost-effective calibration suitable for most industrial applications
• Faster turnaround times
• Supports routine monitoring and general process control
• Provides adequate accuracy for non-critical measurements

What Is ISO/IEC 17025 Accreditation Calibration?

ISO/IEC 17025 is the international standard that evaluates the competence of the entire calibration laboratory and documents measurement uncertainty. This standard was developed and published jointly by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) to provide global guidelines for laboratory quality and technical data.

ISO/IEC 17025 evaluates more than the reference standard used during calibration. It also focuses on the entire calibration system, including: 

• Traceability to national or international standards. Ensures every measurement connects to recognized metrology institutes, improving confidence and global consistency.
• Defined and documented measurement uncertainty. Gives a clear understanding of the precision of each measurement, helping you evaluate risk and meet regulatory or validation requirements.
• Competence and training of personnel. Reduces the likelihood of human error by ensuring calibrations are performed by qualified, regularly evaluated technicians.
• Validated calibration methods. Demonstrates that calibration procedures are tested, repeatable and proven reliable, strengthening confidence in results.
• Environmental controls (temperature, vibration, humidity). Prevents outside conditions from influencing calibration readings, improving stability and repeatability.
• The quality management system. Ensures proper documentation, corrective actions and process controls are in place, which is important for audits and long-term reliability.
• Regular audits by independent accreditation bodies. Provides ongoing, third-party verification that the laboratory continues to meet ISO/IEC 17025 standards over time.
• Accreditation from ANAB or other ILAC-recognized bodies. Ensures calibration results are accepted internationally, reducing duplicate testing and simplifying compliance across borders.

ISO/IEC 17025 Key Benefits: 

• High level of confidence in measurement accuracy
• Accepted internationally without the need for retesting
• Comprehensive documentation for regulatory audits
• Detailed uncertainty reporting

Figure 1: ISO/IEC 17025 and a NIST Traceable Calibration Comparison Chart

Which calibration method do I choose?

Choosing the right calibration standard depends on your application’s risk level, regulatory oversight and accuracy requirements.

Figure 2. Which method to choose?

Examples of instruments commonly used in calibration work

Reference instruments play an important role in both ISO/IEC 17025 and NIST traceable calibrations. For instance, test gauges and handheld calibrators serve as comparative tools during calibration or verification routines.

The following are examples of Ashcroft instruments that can be calibrated to either ISO/IEC 17025 or NIST standard, depending on what the user requests from the calibration lab.

The Ashcroft®1082 Test Gauge is an ASME Grade 3A reference gauge that provides accuracy to ±0.25% of span. Its mirror-band dial and knife-edge pointer help eliminate parallax error, which is an important factor when performing high-precision comparisons.

The Ashcroft®1084 Test Gauge is a compact test gauge with ±0.5% of span. It is used for field verification of installed pressure devices and includes a protective carry pouch, making it convenient for technicians performing on-site NIST traceability checks.

The Ashcroft® ATE-2 Handheld Calibrator is a digital, multi-function instrument that can measure pressure, temperature, voltage and current, and offers accuracies down to ±0.025% of span depending on the pressure module. It is used for documenting calibration points during field work.

Ready to learn more?

Understanding the difference between ISO/IEC 17025 accreditation and NIST traceable calibration helps ensure your instrument calibration strategy matches your quality and regulatory requirements. The right choice will depend on how critical the measurement is, what level of documentation your process requires and whether uncertainty analysis is necessary.

If you still have questions, contact us to speak to a product expert. In the meantime, take a look at the additional articles and resources below.