Abstract
Microplastics (MP) are a pollutant that can be found in all marine ecosystems. Currently one of the most used forms to classify them is through their size. However, the current size categories in use cover an extremely wide range of sizes and are not based on a biological or physical basis. Thus, here we propose to harmonize the MP size categories with the ones already in used on plankton research for more than 120 years. This will allow the implementation of more refined MP size classes that are connected to a biological reality and will also enable the comparison of a myriad of literature on plankton research with the new work on MP.