An apparatus and method for determining an amount of chemical input, and more particularly to an apparatus and method for determining the amount of a chemical to be added, which is necessary to achieve target water quality, wherein a required chemical concentration can be accurately calculated based on the temperature of the water and the target turbidity of the water includes an information-receiving unit configured to receive at least one of environmental information, chemical information, and water-quality information of the water present in a specific area and a chemical input determination unit configured to derive a multiple regression equation based on the received environmental information, chemical information, and water-quality information and to determine the future input of a chemical that is added to satisfy a target turbidity of the water present in the specific area based on the multiple regression equation.