[Brian Johnson]

  I am doing a lab to determine the iodine values of several types of oils, and one of the procedure is dissolving oils in chloroform. I wonder what should be the ratio between them

[Arkcon]

The protocol should specify.  However, chloroform is the solvent, its what the reaction is dissolved in.  You need "enough", depending on the particulars of the reaction. 

How to solve this for yourself:  look up the reaction that will happen.  Determine how much iodine you will need for worst case and best case scenario.  Consider what reaction vessel you'll need.  This will give you hints into how much solvent you need.