Particle formation by flame spray pyrolysis is investigated theoretically and compared with particle size distribution data of ZrO2 production at 100-300 g/h. Spray droplet size distributions as well as droplet and gas velocities are measured by phase Doppler anemometry along the axis and radius of the solid-cone-type spray. Multicomponent droplet combustion is simulated, accounting for droplet polydispersity, transport, and evaporation. The dynamics of the product particle size distributions are investigated, accounting for coagulation and sintering by population balance equations. The effect of the initial droplet size and liquid feed rate on the evolution of the product particle size and polydispersity is analyzed.