Compression of the O-ring cross section (O-ring compression). The compression value specifies the deformation of the O-ring cross section in radial or axial direction relative to the cross section of the uncompressed O-ring.

Compression (in %) = · 100

Standard values in mechanical seals lie between 5 and 10% for dynamically loaded O-rings and between 10 and 20 % for statically loaded O-rings. The tolerances of all the elements involved must be taken into account in design calculations of the compression.