According to an example, an arrangement of parts to be printed in a build envelope of a three dimensional (3D) printer may be determined through identification of a plurality of parts to be printed and generation of a respective virtual bounding box for each of the plurality of parts. In one example, a determination may be made that a total volume occupied by the generated virtual bounding boxes falls below a predetermined threshold of the build envelope volume and an arrangement of the virtual bounding boxes inside the build envelope that results in a total height of the virtual bounding boxes being minimized may be determined, to enhance efficiency in printing of the plurality of parts by the 3D printer.