Measurement Uncertainty · 4 min read
CMC (Calibration and Measurement Capability) Explained
CMC is the number on an accreditation scope that tells you how good a lab really is at a given measurement. Once you can read it, comparing labs gets much easier.
Part of our guide to Measurement Uncertainty & Traceability.
What CMC is
Calibration and Measurement Capability is the smallest measurement uncertainty a lab can achieve for a specific measurement under near-ideal conditions, as assessed by its accreditation body and published on its scope. It represents the lab’s best case; the uncertainty on your actual certificate may be larger once the real instrument and conditions are included.
How to use it
Compare a lab’s CMC for your measurement against your tolerance. A CMC that is a small fraction of your tolerance means the lab can give you a healthy test uncertainty ratio and confident conformance decisions. If the CMC is close to your tolerance, look for a more capable lab or expect guard-banded results with less margin.
Common questions
Is the certificate uncertainty the same as the CMC?
No. CMC is the best achievable uncertainty on the scope; the reported uncertainty on your certificate includes contributions from your specific instrument and conditions, so it is equal to or larger than the CMC.