How to resize an object in Zbrush and export it in real world units?

• The actual size depends on three things:
  1. Size in ZBrush
  2. Export Scale value (Tool->Export->Scale)
  3. Unit in the target software. Maya’s default unit is cm.
• Change the size of the object:
  Go to Tool -> Geometry ->Size -> Modify the XYZ Size value (this is the largest of the three (x,y,z)).
  This is an independent unit. (By the way ZBrush really likes if the object size is about 2 unit.)

The expression is this:
Value Wanted (the true size of the object in Maya) = Size (in Zbrush) × Export Scale (in Zbrush)

For example:
184 cm high character = 1.84 unit (size in ZBrush) × 100 (Export scale in Zbrush)
or
100 cm high character = 2 unit (size in ZBrush) × 50 (Export scale in Zbrush)

This is true in every export scenario (GoZ, FBX export, OBJ export)

Cheers, D