A program is described for the shape analysis of backscattering spectra. The theoretical curve is a result of the convolution product of a straight line with a gaussian function of variable full width at half maximum approximating the variation of the energy straggling. The calculated spectrum is adjusted to the experimental points by the x 2 method. Improved precision of deduced parameters leads to better results in further calculations of energy loss and especially energy straggling of charged particles in thin films.