Available analytical techniques do not allow for a complete characterization of the 1 to 5000 µm Microplastic (MP) continuum. Spectroscopic techniques provide information on MP polymer identity and 2D morphological aspects but not on the third dimension: depth. Based on 2D shape characteristics and depth, particle volume can be estimated, which is crucial for accurate particle number to mass conversions and risk assessments that use ingested particle volume as an ecologically relevant metric. Depth (or height) and estimated volume usually are estimated using various approaches, which however rarely have been validated. Here we evaluate a new validation approach that uses the collective volume of environmentally relevant MP mixtures, rather than validation based on volumes of individual particles. A sample of MPs from Singapore's beach was divided into three groups: