An scanning probe microscopy-based approach to quantify the dielectric constant of insulating films under environmental conditions is proposed. The method is based on the electrowetting effects on the adhesion force behavior between a conductive atomic force microscopy probe and the dielectric surface under study. By carrying out a parabolic fitting of the experimental data, parameters containing interfacial and dielectric properties of the sample are obtained. This provides a simple approach to estimate the value of the dielectric permittivity if the film thickness and the surface water contact angle are known. This method does not require any geometrical calibration of the probe as proposed in previous procedures. However, measurements have to be conducted under adequate values of relative humidity (in the range from 40 to 70% approximately) in order to guarantee the stability of the adhesion force measurement. The validity of the approach was verified in a poly(methyl methacrylate) layer and two SiO2 films, obtaining excellent agreement between the reported values in the literature and the experimental results obtained.