The production of highly accurate components of renewable energy systems such as Wind Energy Systems (WES) or Tidal Power Generators (TPG) puts mandatory constraints in the verification procedures related to 3-D geometry for the tolerance of size, form, waviness and roughness. More information concerning geometric flank deviations, the case hardening and surface roughness properties are requested. This paper focuses on the calibration and measurement of large gears used in gearboxes of WES and TPG. One major issue ensuring traceability of these measurements is the lack of appropriate gear measurement standards. One large ring gear measurement standard was developed recently by the Physikalisch-Technische Bundesanstalt (PTB). In this contribution, the ring gear and its calibration on a large coordinate measurement machine (CMM) are described. Tactile measurement results are presented and put into context with calibration values from PTB. Furthermore, optical measurement results using a new interferometric point sensor, developed by Hexagon, are presented.