Wallpaper fitting begins with shape, then pixels. Portrait phones, near-square tablets, 16:9 laptops, and ultrawide monitors remove very different regions from the same source. If the subject fills a portrait canvas edge to edge, even an 8K file will lose its head and tail or create awkward empty bands on a landscape screen.
Build a generous master first: keep the subject complete, make the background extendable, and place defining details safely away from every edge. Derive three crop families. On a phone, position the visual center below the clock. On a tablet, preserve vertical and horizontal flexibility for rotation. On a desktop, move the subject away from the area usually covered by working windows.
Do not stop at zooming inside a photo viewer. Install each export as a real lock and home screen. Check operating-system scaling, depth effects, the Dock or taskbar, and desktop icons. Apple's own workflow allows wallpaper editing from the Lock Screen, a useful reminder that final cropping belongs to the device experience rather than the source image alone.
Clear file names—phone-lock, phone-home, tablet, and desktop—also prevent friction. The value of a multi-device asset pack is not merely more pixels; it is that each file has already resolved crop and interface conflicts. If you must start with one version, choose the device you activate most often.