It would be great to have a new help article, which shows the dimensions of the Landing Page templates provided in the Library. I’ve seen it asked a couple times in the discussions section. Sort of like this (example facebook):
Firstly I would like to apologize for the delayed response. Secondly, I agree, having the dimensions documented in a graphical manner would be very useful. I will ensure that this is passed along to the appropriate people here at Marketo and that it be worked on.
Jessica, We are publishing the images sizes for our email templates in a ReadMe file which you get when you download the program. We'll publish a ReadMe for our landing pages as well going forward.