Simple way to determine the percent of various screen real estate commitments in competition?

In short, I want to analyse a number of web pages, let's say, specifically homepages of Vox and HBR (but also a dozen others).

1) I want to figure out how much screen real estate they're giving to different categories, mediums, ads, navigation, etc. Eg, 25% of a the page is dedicated to featured stories, 15% is dedicated to audio/video.

2) I might break it up between above and below the fold, or hypothetically even try ways of weighing it according to a scroll map.

What's one way to do (1)? What might be a simpler way?