A little more formally, with sources: Density of plastic: https://omnexus.specialchem.com/polymer-properties/properties/density https://omnexus.specialchem.com

A little more formally, with sources: Density of plastic: https://omnexus.specialchem.com/polymer-properties/properties/density https://omnexus.specialchem.com/polymer-properties/propertie... - Eyeballed at 1.2 g/cm^3 Plastic waste, lifetime: https://advances.sciencemag.org/content/3/7/e1700782 https://advances.sciencemag.org/content/3/7/e1700782 - 6.3 megatonnes (2017) 6.3 Mt / (1.2 g/cm^3) = 5250000 (5.25 million) m^3 = 0.00525 km^3 You were right! My math was way off. Thanks for noticing. This is a great demonstration of peer review :)