For example A greengrocer sells two types of orange which are big size and small size . While we speak about which orange I need , I say sentence below;

> I need small size of this ( by showing big size ornge as I couldn't see the small size orange )

or 

>I need this in small size ( by showing big size orngeas I couldn't see the small sized orange )


I know there are more simple ways to explain this situtaion but I try to learn difference between two phrase .What I wonder is that does both sentence have same meaning ?I mean'' in small size or small size of'' cause sentence mean different ?