50,000 contact cards...
https://support.apple.com/en-us/HT202158
iCloud: Limits for Contacts, Calendars, Reminders, and Bookmarks
Contacts, Calendars, Reminders, and Bookmarks might have issues keeping changes up to date across your devices if you exceed one or more of the limits listed below.
To help iCloud keep your information up to date, keep your data within the following limits:
Calendars and Reminders
Contacts
Bookmarks
https://support.apple.com/en-us/HT202158
iCloud: Limits for Contacts, Calendars, Reminders, and Bookmarks
Contacts, Calendars, Reminders, and Bookmarks might have issues keeping changes up to date across your devices if you exceed one or more of the limits listed below.
To help iCloud keep your information up to date, keep your data within the following limits:
Calendars and Reminders
- Total number of calendars, events, and reminders: 25,000
- Maximum combined number of calendars and reminder lists you can have: 100
- Maximum size of all calendar and reminder data (not including attachments): 24 MB
- Maximum size of all event attachments: 300 MB
- Maximum size of a calendar event including attachments: 20 MB
- Maximum number of attachments per event: 20
- Maximum number of attendees you can invite to an event: 300
- Maximum number of people with whom you can share a private calendar: 100
- Maximum number of characters in a reminder title: 100
Contacts
- Total number of contact cards: 50,000
- Maximum size of a contact card: 256 KB
- Maximum size of a contact photo: 224 KB
- Maximum size of a contact group: 256 KB
- Maximum size of all contact cards:
- Card text: 24 MB
- Card photos: 100 MB
- Supported file types for a contact photo: JPEG, BMP, PNG, GIF
- vCard import limits:
- Total number of vCards: 50,000
- Maximum size of a vCard: 256 KB (photo + text)
- Maximum photo size for a vCard: 224 KB
Bookmarks
- Total number of bookmarks: 25,000
- Maximum size of a bookmark: 4 KB
- Maximum size of all bookmarks: 24 MB