Update using cellular data

Whilst Apps can be updated over a Cellular connection - for System Software updates, iPad can only be updated over a standard WiFi connection, or updated by a PC or Mac using iTunes or Finder - over a USB connection.

If you are using a mobile broadband Router (sometimes known as MiFi) - and using its WiFi hotspot or USB connection with iPad - a system software update may be possible over Cellular. iPad “sees” a WiFi connection - and allows the update to proceed.

iOS/iPadOS devices cannot be updated over a cellular connection as the “update” often includes an update to the Cellular Radio - and this cannot be updated whilst the connection is active. A near continuous network connection is required during a System Software update, the connection only being “dropped” during the “re-flash” phase of the update process.

In summary, the size of the System Software update is largely immaterial. The restriction that prevents update over Cellular is actually technical in nature..

There are many types of things that can be updated: iPadOS itself, individual apps, and their data. Each of those would involve a different amount of data. Full system updates can run into gigabytes; apps can be hundreds of megabytes or even a few gigabytes; app data can be any size.