A general description and analysis of the hyperbolic tangent distribution family are presented. Analytical formulae are given for both the cumulative and frequency functions of the distribution, as well as for the ordinary moments of whole order. A linear transformation of the size coordinate axis is applied by means of which the distribution function can be located appropriately over the interval between the observed smallest and largest sizes of particles during the fitting procedure. Including the parameters of this transformation, the distribution family possesses four parameters, which allows for effective fitting to experimental size distribution data. A two-level fitting procedure has been developed which was tested by using simulated noisy data. A number of distribution functions (log-normal, Rosin-Rammler, and beta distributions) may also be described well by hyperbolic tangent distribution functions, so that it provides a convenient method for comparing measurement data described quantitatively in different ways.