A method for ascertaining an expected contour of a mobile or stationary device for avoiding collisions, using at least one control unit that is internal external to the device includes: obtaining a movement trajectory of the device, which contains probability densities based on state estimation, at least based on expected values and covariances; obtaining a base polyhedron and an approximate contour of the device having a limited number of corners, a confidence interval within which a collision with the static and dynamic surroundings of the device is to be avoided being defined; transforming the base polyhedron to the at least one probability density of the movement trajectory that describes the state estimation; and, for each corner of the transformed base polyhedron, computing a transformed device contour, and ascertaining the expected contour of the device with inclusion of all transformed device contours.