In this work, we demonstrate the controlled synthesis of silica nanoparticles as small as 30 nm (±5 nm) and as large as 250 nm (±30 nm) in minutes using surfactant free, microwave-assisted synthetic techniques. Proper choice of solvent, silicic acid precursor, catalyst, and microwave irradiation time were the variables used to control nanoparticle size and, ultimately, overcome the previously reported shortcomings of using microwaves for silica nanoparticle synthesis. In these reactions acetone, a low-tan δ solvent, mediates the condensation reaction, while selective absorption of pulsed microwave radiation by the precursor promotes nanoparticle growth. Dynamic light scattering data, scanning electron micrographs, and transmission electron micrographs of the reaction products show that the size, shape, and granularity of the silica nanoparticles are highly dependent on reaction conditions. These microwave methods have utility for mass production of silica nanoparticles or other nanoparticles by flow-through microwave synthetic methods for industrial applications, as well as a facile method for encapsulating or embedding materials with silica for improved functionality and stability.