PSA
There is an article on the WTOP DC news site. It attempts to show the crowds that have been at the different inaugurations.
link: How did Trump’s inauguration crowd compare? (Photos)
They even show other DC Mall confluences, like the Million Man March, Oct 1995 and America's 200th BD, July 1976.
The odds of your attempt to guesstimate the crowd numbers can be compared to the guy at the county fair trying to win a Kewpie Doll for his girl playing the Ring Toss..
OR guessing the number of peanuts in a 55 gal drum.
YMMV, Vastly
PS: I think the WTOP article is bias,, but they tried..
Here is one slide,, Look at it, make your own observations and GUESSES.