The size reported on the App Store (204MB as of today for PayPal version 6.8.0) does not take into account App Thinning.
The App Thinning process only delivers the parts of the app required by the device. For example, the launch screen for iPad would not be downloaded onto my iPhone; and the 32-bit binary would not be downloaded on a 64-bit device. For my iPhone 6s, the actual installed size is 131.7MB (see Settings > General > Storage & iCloud Storage > Manage Storage).
If I download the PayPal app through iTunes it is delivered as a compressed .ipa archive of 85.8MB. I can inspect this archive as detailed in another answer of mine: What is the iOS url scheme for Apple’s Numbers app? Doing so I can see that the extracted app total of 152MB is composed as follows:
The GrandPerspective app can also give a visual representation of the number of files that comprise the app and how they vary in size:
Originally published at www.quora.com.