Sentence:  [The researchers] noticed many of their pieces of [plastic marine] debris sported surface pits around two microns across. Such pits are about the <WSD>size</WSD> of a bacterial cell. Closer examination showed that some of these pits did, indeed, contain bacteria, [...]. 
Meaning of the word marked with <WSD> tags:  The dimensions or magnitude of a thing; how big something is. (from 15th c.)