[AlphaScent]

So without getting into a great debate about partition coefficient and how smaller volume extractions are better then large volume ones;  I understand the math that is involved.

But practice is so much different than by the book.  What is your personal rule of them when doing an extraction?

Mine is 10% (ex. 10 mL of ether to 100 mL of aqueous material)

[Doc Oc]

I typically use more of a 1:1 ratio.  I do 1 extraction for pilot/exploratory reactions and 3 for something I'm actually trying to get isolated yield on.

[Archer]

I agree, one for crude based on what I am extracting and from what. And 3 for "best" conditions.  I usually determine the diminishing returns on aliquats of the extraction solvent if I am concerned (i.e. check each wash before combining them.

Ideal situation on pilot scale (100-500g product) is counter current extraction on a continuous process. Much lower solvent consumption.