How this tool reads your file
The image is decoded in the browser and its intrinsic width and height are read directly from the decoded bitmap, which is the size that actually matters on screen.
Dimensions, aspect ratio and DPI
Width and height in pixels are the only numbers that matter for screens. DPI or PPI values stored in a file only affect how large the image prints; they have no effect on a web page. The aspect ratio shown alongside the dimensions is useful when you need to match a layout — 16:9 for video thumbnails, 1:1 for avatars, 4:5 for portrait social posts.