An extension of a previous method for designing continuous thickeners is presented. The previous method was based on data obtained for batch testing, where the discontinuity heights corresponding to the supernatant-suspension and to the top of the sediment are known at different values of time. From the data batch testing, the area per unit of volumetric flow and the sludge height can be calculated for different underflow solids concentrations in continuous thickeners at a specific interval. This interval can be increased allowing the sediment to rise almost to the top of the cylinder, where the testing is carried out. The method of design has been tested with thickeners at laboratory scale working semicontinuously, with periodic withdrawals of sludge and supernatant and feeding of suspension.