Estimate storage used by apps.
App storage splits into the installation itself and the data it accumulates, and on a well-used phone the second is usually larger. Social, streaming and mapping apps cache aggressively, so a hundred-megabyte install can sit on a gigabyte of cached media. Separating the two shows where space actually went and which half you can reclaim without uninstalling anything.
Storage split
Binaries GB = apps x average app size MB / 1024; cache GB = apps x average cache MB / 1024
Device impact
Share of device storage = total app GB / device capacity GB x 100
The operating system and preinstalled software take a slice, and manufacturers quote capacity in decimal gigabytes while the system reports binary gibibytes. A 128 GB device typically shows around 119 GB usable before anything is installed.
Generally yes — cached data is rebuilt on demand. The exception is offline downloads such as saved music, maps or video, which are stored in the same place and are genuinely lost.