Abstract: The disclosure features calibration fluids that include a plurality of beads, such as cellulose, silica, poly(methyl-methacrylate) (PMMA), melamine, cross-linked agarose, polyvinylacetate (PVA), and/or polystyrene beads, where the beads are sized and colored to represent at least one type of blood cell; and a carrier fluid, that can include a polymer or polymerizing matrix, e.g., a water-soluble resin, e.g., an acrylic or polyurethane water-soluble resin or a starch or a cellulose, serum, and/or one or more or sugars. The disclosure also features methods of using the calibration fluids to calibrate automated sample preparation systems, such as automated hematology analyzer systems, e.g., image-based hematology analyzer systems.