Estimation of the tray (plate) efficiency is the basis of trayed column design. A newly introduced parameter "normalized efficiency" (eta) is compared to the stripping factor (lambda) in order to derive a correlation which can be useful in engineering practice. The proposed correlation is based on the numerous data gathered from various literature sources describing distillation, absorption, and stripping (desorption) columns and covering sieve, tunnel, bubble-cup, uniflux, and jet trays, in the range lambda = 0.0391-2196. The final form of this correlation is eta c = {1/1 + 1.5 lambda(0.9) for lambda <= 1 lambda 0.3/1.5 + lambda(0.3) for lambda <= 1 with correlation ratio Theta = 0.883 and standard deviation Delta(av) = 13.1%.