Center-of-mass perception in dot patterns arranged into triangular and quadrilateral configurations was investigated. In Exp. 1, the length, orientation, and direction of dots forming right triangles were varied. Errors in center-of-mass perception by 19 participants increased with the length of the triangles. In Exp. 2, 27 participants estimated the centers of squares and rectangles made up of four dots. Accuracy was best for squares that contained greater reflective and rotational symmetry. The orientation of responses was generally downward in both experiments, indicating a gravitational influence. The results are consistent with a process model by which observers use internal pattern structure like medians and axes when estimating the center of an object.