A simple explicit formula for evaluating the total capacity of chilled-water cooling coils under wet conditions is reported in this paper. The formula is developed through theoretical and analogical analysis from a practical viewpoint. With the formula, a wet coil’s total cooling capacity can be predicted straightforwardly, given the inlet air and water conditions. The formula was cross-validated against a set of catalog performance data from a series of fan coil unit (FCU) coils and simulated performance data from a series of air handling unit (AHU) coils. The mean errors in the calculated results of the present formula did not exceed 5% in the training and test sets for each coil, showing it has good accuracy and generalizability over a wide operating range and various coil types. This formula is expected to have wide applications in energy simulation and control optimization of building air-conditioning systems.