Their market cap today is ~5.6B at $18 a share. Jumping back to December 7, they were worth $23, so ~7.3B market cap. So, close to 4% of outstanding shares.
Agreed this metric is better, but the article also notes that these two firms own 70% of SolarWinds so any meaningful sale would be large by this measure I think?
SWI has 53 million floating shares, resulting in 53m*23= $1.2 billion today.
So a quarter of float traded. That is crazy movement.