The invention concerns a single-particle inductively-coupled plasma (ICP) mass spectrometry particle sizing and counting method comprising providing or receiving an intensity-versus-counts histogram of particles detected using an ICP mass spectrometer, the intensity representing particle detection and the count representing particle detection frequency; providing or receiving mass flux calibration data or calibration curve data relating a value of the intensity measurement or data of the ICP mass spectrometer to a mass of material detected per acquisition interval or dwell time; determining a particle mass of the particles detected using the mass flux calibration data or the at least one mass flux calibration curve data, determining a particle volume of the detected particles using the determined particle mass, and determining a particle size of the particles detected using the determined particle volume of the particles detected and a determined or attributed geometry or shape of the detected particles.