Actually it is not standard for any category of cells. It varies according to whether the donation may have been cut short due to problems, and due to the amount of excess fluid removed. And since, we rarely give whole blood (except in "the field" where measurement would be difficult, it depends on amounts removed due to leukoreduction, and removal of plasma for FFP. In addition, though plasma pheresis is preferred for transfusion, there are still places that use random donor, which is removed from the RBCs.
An average PRBC unit is 275-475mLs. Some hospitals, have volume depleted units for use with patients that have fluid status issues...more of the excess fluid has been removed. Also, patients that require blood run very slowly, and the units are divided.
Platelets - one unit pheresis (single donor) - anywhere from 175mL - 500mL. If 500mL, then it usually is in two bags. Platelets from random donors vary even more widely.
FFP - 200mL to 400mL.
Granulocytes - usually 225mL to 400mL