Storage size calculations

You can learn about the costs of this storage at Firestore Enterprise edition pricing.

String size

String sizes are calculated as the number of UTF-8 encoded bytes + 1.

The following are stored as strings:

• Collection name
• Field names
• String field values (including _id)

For example:

• The collection name tasks uses 5 bytes + 1 byte, for a total of 6 bytes.
• The field name description uses 11 bytes + 1 byte, for a total of 12 bytes.

Field value size

The following table shows the size of field values by type.

For example, a boolean field named done would use 6 bytes:

• 5 bytes for the done field name
• 1 byte for the boolean value

Document size

The size of a document is the sum of:

• The string size of the collection name
• The sum of the string size of each field name (except _id)
• The sum of the size of each field value (including _id)
• 48 additional bytes

This example is for a document in collection tasks:

{
  "_id": "my_task_id",
  "type": "Personal",
  "done": false,
  "priority": 1,
  "description": "Learn Cloud Firestore"
}

The total size of the fields is 78 bytes:

So the document size is 6 + 78 + 48 = 132 bytes:

• 6 for the collection name
• 78 bytes for the fields
• 48 additional bytes

Index entry size

The size of an index entry in an index is the sum of:

• The string size of the collection name
• The size of the _id field value
• The sum of the indexed field values
• 48 additional bytes

Consider a document in the tasks collection:

{
  "_id": "my_task_id",
  "type": "Personal",
  "done": false,
  "priority": 1,
  "description": "Learn Cloud Firestore"
}

For an index on the done and priority fields (both ascending), the total size of the index entry in this index is 70 bytes:

• 6 bytes for the collection name tasks
• 11 bytes for the _id field value
• 1 byte for the boolean field value
• 4 bytes for the 32-bit integer field value
• 48 additional bytes

For sparse indexes, if a document doesn't include any of the fields, then no index entry is created. If a document contains at least one of the indexed fields, an index entry is created with absent indexed fields set to NULL.

What's next

Learn about Firestore Enterprise edition pricing.