Is it possible to convert unit of measure from pcs/units to gm/kg ?

Example,

I have one product say, Apple Jam

1. I receive this product from supplier as Carton (2 pcs)

2. Each pcs/jar contain 2.5 kg of jam.

3. I need to consume/issue/bom this apple jam in gm.

4. I created one UoM Carton 2 

5. I create UoM Jar 2.5 kg
   

6. How can i map these two?

7. What is the use of field `weight' and `Volume` in Product master ?