To determine the number of tilepacks required for a region, you need to download the tilepacks. Currently, there isn't a definitive way to determine the number of tilepacks before downloading. You can check the required number of tilepacks by looking at progress.required while the download is in progress. For more information on how to implement this, see the OfflineManagerExample.
For more information on downloading tilepacks to make your maps available offline, see Maps SDK Offline documentation: iOS, Android