Abstract: An apparatus and method for determining the particle size distribution of a plurality of particles in a sample, the apparatus comprising a particle charging chamber for charging the particles in proportion to a dimension of the particle, such as surface area, and from which charged particles exit primarily one-at-a-time, a collector electrode for catching the exiting particles, and a charge-measuring device that produces an output with a value representing the measured particle charge. The particle charging chamber may comprise a number of electrodes and a DC voltage source connected to the electrodes. A conversion device, such as a computer, may receive the output from the charge-measuring device and convert measured individual particle charge data to a particle surface area distribution. The apparatus may further comprise light beams and light detecting means between the exit of the charging chamber and the collector electrode, for determining particle terminal velocity as it exits the charging chamber.