For experimental control of particle size, the number of experimental control variables to control crystal nucleation is limited. For controlled batch precipitations, these are temperature, solubility of the crystals, reactant addition rate, and the presence of ripeners and restrainers in the reaction medium during the nucleation phase. The author will present the balanced nucleation and growth (BNG) model, which provides quantitative directions how these factors affect the crystal size and number. These experimental parameters can be incorporated in the lab, research, product development, and manufacturing phases of crystallization. They further provide quantitative guidance for scale-up. Examples will be shown.