Abstract The attainability set is defined to be a finite-dimensional integral-type image of the set of all absolutely continuous scalar functions of time whose derivatives take values in a given interval. For a class of control systems with scalar controls restricted to the above interval (the class comprises, in particular, some bilinear systems), the attainability set has the traditional meaning. A method of finite-dimensional parametrization of the attainability set is described. The parametrization is universal, i.e., the same for all attainability sets of a fixed dimension. For the case of control systems, the result provides an upper estimate on the number of switchings sufficient to bring the system to an arbitrary reachable state at a prescribed time.