Web resolution

On screens, what matters is an image’s pixel dimensions, such as 1200 × 1200. With too few pixels, edges look blocky, like the left ring; with enough, they look smooth.

You may hear that web images should be 72 PPI. The PPI number stored in a file does not change how a browser shows it; only the pixel dimensions and the display size do.

High-density phone and laptop screens pack more pixels into the same space, so images need more pixels to stay sharp. Balance sharpness against file size, since bigger images load slower.