Do you need a lot of Megapixels?

Of course, everyone loves a lot of megapixels in their camera :D

From the start of my interest in photography, i knew that megapixels are not all important even if many of camera (and phones) manufacturers advertise it almost as main thing. But i never really thought about the the math behind it (and yes there is math there :) ). Just wanted to post a photo where i would like to have more of them, but finished by doing some research.

If we are talking about printing size one thing that is often forgotten is the viewing distance and what are our eyes capable of seeing. And there is a formula to it:

ppi(pixels per inch)=1/((viewing-distance-in-inches x 0.000291)/2)

so if you want to print 4 by 6inch photo (roughly 10 by 15cm) if you would look at it from 2 feet (24 inches) away (60cm). 1/((24 x 0.000291)/2)=286.37 so you will need around 300 ppi for a nice print. When you transfer that in camera megapixels 3 megapixels are more than enough.

But you want to print a billboard, but you never look at the billboard from a 2 feet (60cm). Let's say that you look at the billboard from a 65 feet (20 meters).
1/((780 x 0.000291)/2)=8,81. So in theory you could print a billboard from a 1 megapixel camera.

So why would you want more megapixels? That is the reason i started this post.
I don't crop often a lot, i have nothing against it i just try not to. Most of the times when i crop it's because of candid shots in action due to lack of quality zoom lenses (low f stop primes are more affordable :) ) But this is a shot where i would love to have a 50 megapixels camera.
It is a lucky shoot and i almost missed it while making the star trails.

I think it could have been a really interesting shot, with the bird flying through if i had the possibility to crop. But due high ISO and not so much megapixels it is just something that it could have been.