J. Randall Murphy
I may have just happened upon outdated papers and references. This article says they changed the definition in 2006: "
The term ‘asteroid’ had been loosely used to refer to almost all small bodies that go around the Sun. It was not until in 2006 when the term was limited to what it means today due to the introduction of the term ‘small solar system body’ or SSSB that covers both comets and minor planets." Definition & Answers About Asteroids – Terms in Astronomy Asteroid
Here's an example where they say most are the size of gravel. Asteroids
Here's another one out of NASA saying that they can be as small as pebbles: https://nssdc.gsfc.nasa.gov/planetary/text/asteroids.txt
I've been trying to avoid using Wikipedia, but obviously I should cross reference there too. What's really weird is now I can't find any of the articles that said, "ranging in size from grains of sand to several hundred kilometers" It's like I've been Mandelafied or something. I mean there were several articles that came up with the same description, and now I can't find any of them. Why me? I really must start tracking my sources so I don't have to relocate this stuff when there's an inconsistency like this.
As an aside, here's an interesting PDF on the definitions controversy for planets: https://arxiv.org/ftp/arxiv/papers/0810/0810.0993.pdf