What this article did really well is explain how the size of a round is tied to its valuation. I often hear people wonder why a company raised so much or so little, whereas in reality, it was not their choice - how much they raised was dictated by what they were valued at and the ownership percentage the VC was targeting (which does vary, but like Augie said it's often in the 15-30% range).

What I wonder is if the pro rata rights play a role as well. When 30-40% of a later stage round is reserved for existing investors, will that have a positive or a negative impact on the valuation?