I figured it'd be pretty straightforward:
Get total bits by converting bytes to bits
Convert download time to seconds
Divide file size by time to get bps
So I went to this website:
I entered my numbers in the "reverse DL" section to get the results and it differed from what I calculated.
Here's what I did for a 20MB file:
20MB * 1024 = 20480000000 bits
5:20 = 230 seconds
20480000000 / 230 = 89Kbps / sec
The website says it's actually 729Kbps per sec...
I need more coffee... missing something simple, I'm sure...