Monodisperse particles are widely used in calibrating instruments that measure size. NanoMicro offers polystyrene size standard particles ranging from 0.10 μm to 200 μm. These size standard particles are NIST traceable microspheres of highly uniform particle size, 1.0% solids, and are supplied as a suspension in 10 mL drop bottles. Particles with a particle size of less than 1 μm were determined by a centrifugal disc photometer (CPS); particles with a particle size of 1 μm and above were determined by the electro-sensing zone method (ESZ) and calibrated by NIST-traceable standard particles.