Based on the doc:

> Websites listed here are downloaded and analyzed with Phantomas. The total weight is counted and then the size of actual content is measured and shown as a ratio.

> For example: If a website has a total weight of 100kb and 60kb are the documents structure, text, images, videos and so on, then the content ratio is 60%. The rest are extras like CSS, JavaScript and so on. It is hard to say what a good ratio is but my gut feeling is that everything above 20% is pretty good already.