If you look in the customize option of the toolbars, the Options tab give you the Toolbar and menu icon size. i suspect the size is represented in pixels (not sure of it).
Best regards,
Michaël.
NX7.5.4.4 + TC Unified 8.3
Win 7 64 bit (Intel(R) Xeon(R) CPU X5650 @2.67GHz)
24.0 GB
NVIDIA Quadro 4000 + NVIDIA Tesla C2050