What is the biggest file on my web page?
One file often accounts for more of a page's weight than everything else combined: a hero photo saved at full camera resolution, a background video, or a bloated script bundle. Finding that one file is the quickest way to make a page faster, because fixing it can halve the download in a few minutes.
Why it matters
Browsers draw the page as files arrive, and the largest file is usually the one visitors are waiting for: the big picture at the top. While it downloads, the page looks unfinished. On a mobile connection a 3 MB image alone can take three or four seconds. Google's Largest Contentful Paint measure, one of the three Core Web Vitals, is very often just the time this file takes.
How to check
Our check lists the largest file it found with its size and address. In a browser's developer tools, open the Network tab and sort by size; the culprit is at the top.
How to fix it
If it is an image, open it and note the width it is displayed at. Resize it to that width (or twice it for sharp screens), save it as WebP or a JPEG at around eighty per cent quality, and re-upload. A 4 MB photo typically becomes 150 KB with no visible difference. If it is a video, do not autoplay it as a background on phones; use a poster image and load the video only when asked. If it is a script, it is usually a page builder or a theme loading its entire library; a performance plugin can often defer it or load it only where needed.
Make this a habit: before uploading any photo, resize it. It is far easier than fixing a library of oversized images later.
Not sure how your own site does on this? Run the free check: it takes about twenty seconds and reports on this and thirty other things.