Monolayers of the long-chain alcohols on water promote nucleation of ice. In order to determine the minimum size of crystalline alcohol monolayer domains that induce ice nucleation, we reduced their size in two distinct ways. One approach encompassed embedding the pure hydrocarbon alcohol, CnH2n+1OH (n = 20, 31), into a matrix of an immiscible monolayer of perfluoro alcohol C10F21C2H4OH, Which is inert as an ice nucleator. The second set of experiments involved the introduction of random defects into the monolayer crystalline domains of C29H59OH through the use of the fully miscible guest alcohol molecule, C31H63OH, as additive. By these methods we estimated that similar to 450 water molecules are necessary to form a stable ice cluster at the onset of induced ice nucleation at a temperature just below 0 degrees C.