ISO 17025 Audit Check List

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The International Organization for Standardization develops international standards for many technical and professional fields. Known as ISO, from the Greek isos, or equal, ISO standards are used as guidelines for compliance. ISO 17025 provides guidelines for calibration and testing facilities. These facilities are in turn audited and certified as ISO compliant by the American Association for Laboratory Accreditation, or A2LA. A calibration laboratory audited and certified by A2LA is considered an accredited laboratory.


All calibrations must be traceable to the National Institute of Standards and Technology (NIST). Traceability means proper calibration techniques with calibrated standards. Each calibrated standard is in turn calibrated by a higher standards laboratory all the way back to NIST. Like a pyramid, NIST is at the top, the calibration laboratory is in the middle and the end-user of the calibrated item is on the bottom.


ISO 17025 requires a certificate of calibration for every item. This certificate includes information about the item calibrated, information about the calibration standards, before- and after-calibration data, calibration and re-calibration due dates, a statement of uncertainty and traceability, information about the calibration laboratory and technician identification.

A calibration label on each item is also required. The calibration label includes the calibration date and re-calibration due date, item identification number and technician’s identification.

Calibration Procedures

All calibrations require a written calibration procedure. This procedure must be compliant with nationally and internationally recognized methods. NIST and the American Society for Testing and Materials (ASTM) International provide many of these standard methods.

The calibration procedure must include the measurement range and tolerance or uncertainty of the item being calibrated and of the calibration standards. The capabilities and specifications of the calibration standards must meet or exceed those of the calibrated item.

Proficiency Testing

During the ISO 17025 accreditation process, each technician in the calibration laboratory must demonstrate technical proficiency. An evaluator observes the technician perform a calibration procedure, ensuring he is using the proper procedures and techniques. The evaluation also includes proper completion of the calibration certificate and label.