This series of NIST traceable size standards provides an accurate and convenient method for calibrating or checking the performance of laser particle counters used in cleanrooms and other contamination monitoring applications. The products are suspensions of monodisperse polystyrene spheres (PSL) for use in airborne or liquid particle dispersion systems. They are available in a range of sizes from 0.1 to 100µm in diameter. The particles are prepared as low residue aqueous suspensions for minimal background interference, packaged in 15mL dropper-tipped vials. The particle diameters are calibrated by electron or optical microscopy. Each package includes a Certificate of Calibration and Traceability to the National Institute of Standards and Technology (NIST). In comparison with the well established 3000 and 4000 Series products described elsewhere, these product lines are precisely diluted for immediate use in laser particle counters with minimal time-consuming adjustments of concentration.