Sold by piece by weight. Sizes may look similar depending on shape/thickness. Each stone has been weighted. 
SM: 5g to <10g
MD: 10g to <15g
LG: 15g to <20g
XL: 20g to 25g
 
Citrine is a cleaning and condensing energy.  It cleans other energies as it condenses them making them stronger.  Watch out for Citrine and Black Onyx, very strong together.
 
Citrine: A powerful focusing frequency which also cleans and clears away unwanted frequencies and physical issues from such materials as Fluoride, Calcium, and others. (Book II of the Creation series)
 
Stones cranked up by Jay Essex and Diana R. Anaya (Dianimal)