NatureContemporaryglobalhigh confidence

About 94 percent of the plastics in the Great Pacific Garbage Patch are microplastics smaller than a grain of rice.

Notes on verification

94% by piece count is confirmed by the original peer-reviewed Lebreton et al. 2018 study and corroborated by The Ocean Cleanup and multiple independent news outlets. 'Smaller than a grain of rice' is a lay simplification not from the original paper but widely used by secondary sources as a reasonably accurate descriptor of microplastic size.

Sources