We propose a key factor associated with both surface recombination velocity and radiative efficiency of an LED to estimate its chip size-dependent radiative efficiencies. The validity of the suggested factor is verified through experimental comparison between various LED wafers. Efficiencies of micro-LEDs from a blue and two green LED wafers are examined by temperature-dependent photoluminescence experiments. Surface recombination velocities are extracted from chip size dependent time-resolved PL results. Possible explanations on the reason why two green wafers show different properties are also given. With the suggested factor, we can provide more accurate prediction on the chip size-dependent efficiency of an LED wafer.