Only the gzipped size is provided here based on an expert tip.

First Load is the size of the global bundle plus the bundle for the individual page. If a user were to show up to your website and land on a given page, the first load size represents the amount of javascript that user would need to download. If next/link is used, subsequent page loads would only need to download that page's bundle (the number in the "Size" column), since the global bundle has already been downloaded.

Any third party scripts you have added directly to your app using the <script> tag are not accounted for in this analysis

The "Budget %" column shows what percentage of your performance budget the First Load total takes up. For example, if your budget was 100kb, and a given page's first load size was 10kb, it would be 10% of your budget. You can also see how much this has increased or decreased compared to the base branch of your PR. If this percentage has increased by 5% or more, there will be a red status indicator applied, indicating that special attention should be given to this. If you see "+/- <0.01%" it means that there was a change in bundle size, but it is a trivial enough amount that it can be ignored.