The results of research on the creation of a new device for the express determination of seed cotton grade on the acoustic principle of measurements without preliminary ginning of seed cotton samples are presented. A theoretical analysis of the process of passage of sound vibrations through a sample of raw cotton was carried out and an analytical dependence of the output signal of the device on the coefficient of maturity of the fiber, on the parameters of the medium and the design parameters of the measuring chamber of the device was derived. The regression analysis method was used to construct equations of the calibration dependence for various breeding varieties at frequencies of 150 Hz and 200 Hz.