This work proposes a correlation for the specific capital cost of multi-effect distillation (MED) plants, considering their main design options and parameters, such as the number of effects, size/capacity, and heat source temperature. These parameters are varied within a large range to cover as many different cases as possible. The cost correlation decouples the evaporator cost and includes in the expression the ratio of the heat exchanger area to a reference one. This area is calculated using a validated MED numerical model, with the results then processed to produce fitted expressions. Two versions of this correlation with different levels of complexity are proposed, which provide similar results. The results of the improved correlation have been compared with the actual specific cost of a limited number of MED plants for validation purposes. It has been shown that this correlation provides more accurate results in most of the cases, although the sample is small due to limited availability of data from other plants. The specific capital cost of typical MED plants is then examined, presenting the cost when the number of effects and heat source temperature change. These calculations capture the expected trend of the plant cost under different main design options.