Membrane distillation (MD) is a thermally driven separation process, operated at moderate temperature, allowing for the use of waste heat as driving force. While the literature is saturated with lab-scale models, almost none exist for designing a complete MD system. Based on previously published and thoroughly validated models, this work demonstrates a graphical user interface tool, capable of designing a complete membrane distillation system, including all of the supporting equipment and able to predict the price of the obtained distillate for the most commonly studied and used membrane distillation configurations. The user can also optimize the module geometry based on specific requirements. Four different case studies are discussed, ranging from 2 to 1000 m(3) of distillate per day, with final brine salinity up to 20 wt%, feed temperature up to 80 degrees C. The optimal system design for each case is demonstrated. The distillate price varied from 25(sic)/m(3) of distillate for the smallest scale to 2.1(sic)/m(3) for the largest scale. Finally, the reader is presented with a simplified cost model that can be used to quickly estimate the price of the produced distillate at different production scales and concentration factors.