Thank you for that chart!! I think you're right- this does seem a bit smaller than that. I'll look and see if I think one seems close to what it seems like. I'll definitely bring a tape measure tomorrow.
Maybe 29 gallon?
30 inches long, 12 wide, and 18 inches high.
That would be about 2/3 as tall as it is long, which agrees with what I'm seeing in the front view.)
And I think the end view shows it taller than it is wide, although with the angle I am really unsure of that. But if I assume the counter is 2 feet wide (which is a common width for a countertop), and the tank is about half as wide as the counter, then the tank would be about 12 inches wide.