Firestore Document Limit
- Max document size: 1 MiB (1,048,576 bytes)
- Max size of document ID: 1,500 bytes (Document ID must be UTF-8: if using only ASCII characters, it support up to 1500 characters)
- Max size of field name/path: 1,500 bytes, including list/map path. e.g.
person.location.address= 23 bytes - Max size of field value: 1 MiB - 89 bytes (1,048,487 bytes)
- Maximum depth of fields in a map: 20
- Maximum write rate to a document: 1 per second
- Maximum number of index entries for each document: 40,000 (single-field index entries and composite index entries)
- Maximum number of fields:
- Each field is created with 2 index by default (ascending & descending), thus maximum number of fields is 20,000 (limited by max index entries)
- If composite index are used, less than 20,000 fields are supported
- If no index is created (using Index Exemptions), assuming each field is 100 bytes, maximum of 10,485 fields is supported (limited by max document size)
NOTE: I suspect document size include field name + value (I have yet to found a reference or tested on this).
NOTE: Note that each UTF-8 characters could be between 1-4 bytes.
References: