Manufactured stormwater best management practices (BMPs) generally apply one or both of two unit operations to remove particles from stormwater runoff: hydrodynamic separation and filtration. Hydrodynamic separation is best used to remove sand particles, while filtration is used to remove organic particles as well as silt and clay. Many manufactured stormwater BMPs also have a chamber designed to remove floatables, or particles that are lighter than water. The numerous designs and multiple sizes of these manufactured stormwater BMPs suggest the need for scaling criteria to size and apply designs in the field. This paper reviews the scaling criteria research that has been completed, the research that may be adopted from other areas, and the needs for developing scaling criteria in manufactured stormwater BMPs.