Precise quantification of the magnetoelectric coupling strength in surface charge induced magnetoelectric effect was investigated in NiFe/SrTiO3 thin film heterostructures with different ultra-thin NiFe thicknesses through voltage induced ferromagnetic resonance. The voltage induced ferromagnetic resonance field shifts in these NiFe/SrTiO3 thin films heterostructures showed a maximum value of 65 Oe at an intermediate NiFe layer thickness of ∼1.2 nm, which was interpreted based on the thin film growth model at the low-thicknesses and on the charge screening effect at large thicknesses. The precise quantification and understanding of the magnetoelectric coupling in magnetic/dielectric thin films heterostructures constitute an important step toward real applications. © 2013 AIP Publishing LLC.