unit and alternateive unit

 Hi, i am working on an inventory application.

 

i am stuck at the unit conversion , like if a product is in Kilogram, i need to sell in grams or tons, dozen to pcs and  custom pack is also there like a carton may contain 20 pcs and need to sell it in pcs or it may contain 40 pcs. i hope you understand my question,

 

Product table is like

 

ProductID	Name	Rate	Unit	Baseunit	conversion
1	Item A	100	carton	Pcs	20
2	Item B	120	carton	Doz	10
3	Item C	100	Kilogram	Gram	2