Online tool for calculating and designing thermal insulations and their thickness, so users can easily choose proper building insulation. The calculator allows the user to select one of the fifteen compositions that are the most common in building thermal insulation, and choose a particular composition for insulating walls, floors, roofs, soils, basements, etc. It also distinguishes between the type of buildings and individual constructions according to building materials used (wood, concrete, steel structures, etc.). The results are shown in an insulation catalogue.