We describe, first to our knowledge, optical resonances of Transverse Electric (TE) and Transverse Magnetic (TM) wave propagations in dielectric micro-circular-cylinder. New Asymptotic approaches have been developed based on TE & TM waves. Size parameter (pi times diameter divided by wavelength of the light) is phenomenal to demonstrate Whispering Gallery Mode (WGM) in dielectric circular cylinder. The developed expressions for size parameter for both TE & TM waves are very simple and can be used to characterize the resonances in dielectric micro-circular-cylinder. Asymptotic expressions have been developed based on Electro-Magnetic (EM) wave theory derivations which are mathematically robust than existing approaches presented in the literatures, and can be used to develop optical sensors by characterizing resonances in dielectric micro-circular-cylinders. The solutions are shown to be very accurate for large size parameters.