Storage size calculations

This page describes the storage size of documents, document names, fields, and index entries in Cloud Firestore .

String size

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

The following are stored as strings:

• Collection IDs
• String document IDs
• Document names
• Field names
• String field values

For example:

• The collection ID 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.

Document ID size

The size of a document ID is either the string size for a string ID or 8 bytes for an integer ID.

Document name size

The size of a document name is the sum of:

• The size of each collection ID and document ID in the path to the document
• 16 additional bytes

For a document in the subcollection users/jeff/tasks with a string document ID of my_task_id , the document name size is 6 + 5 + 6 + 11 + 16 = 44 bytes:

• 6 bytes for the users collection ID
• 5 bytes for the jeff document ID
• 6 bytes for the tasks collection ID
• 11 bytes for the my_task_id document ID
• 16 additional 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 document name size
• The sum of the string size of each field name
• The sum of the size of each field value
• 32 additional bytes

This example is for a document in subcollection users/jeff/tasks with a string document ID of my_task_id :

- "type": "Personal"
 - "done": false
 - "priority": 1
 - "description": "Learn Cloud Firestore"

The total size of the fields is 71 bytes:

So the document size is 44 + 71 + 32 = 147 bytes:

• 44 bytes for the document name
• 71 bytes for the fields
• 32 additional bytes

Index entry size

Index entry sizes are calculated as follows for single-field and composite indexes.

Single-field index entry size

The size of a single-field index entry depends on whether an index is scoped to a collection or a collection group.

Collection scope

The size of an entry in a single-field index with collection scope is the sum of:

• The document name size of the indexed document
• The document name size of the indexed document's parent document
• The string size of the indexed field name
• The size of the indexed field value
• 32 additional bytes

Consider a document in the sub-collection users/jeff/tasks with a string document ID of my_task_id :

- "type": "Personal"
 - "done": false
 - "priority": 1
 - "description": "Learn Cloud Firestore"

For a single-field index with collection scope that indexes the done field, the total size of the entry in this index is 109 bytes:

• 44 bytes for the document name users/jeff/tasks/my_task_id
• 27 bytes for the parent document's document name users/jeff
• 5 bytes for the done field name
• 1 byte for the boolean field value
• 32 additional bytes

Collection group scope

The size of an entry in a single-field index with collection group scope is the sum of:

• The document name size of the indexed document
• The string size of the indexed field name
• The size of the indexed field value
• 48 additional bytes

Consider a document in the sub-collection users/jeff/tasks with a string document ID of my_task_id :

- "type": "Personal"
 - "done": false
 - "priority": 1
 - "description": "Learn Cloud Firestore"

For a single-field index with collection group scope that indexes the done field, the total size of the entry in this index is 98 bytes:

• 44 bytes for the document name users/jeff/tasks/my_task_id
• 5 bytes for the done field name
• 1 byte for the boolean field value
• 48 additional bytes

Composite index entry size

The size of an entry in a composite index depends on whether the index is scoped to a collection or a collection group.

Collection scope

The size of an index entry in a composite index with collection scope is the sum of:

• The document name size of the indexed document
• The document name size of the indexed document's parent document
• The sum of the indexed field values
• 32 additional bytes

Consider a document in the sub-collection users/jeff/tasks with a string document ID of my_task_id :

- "type": "Personal"
 - "done": false
 - "priority": 1
 - "description": "Learn Cloud Firestore"

For a composite index with collection scope that indexes the done and priority fields (both ascending), the total size of the entry in this index is 112 bytes:

• 44 bytes for the document name users/jeff/tasks/my_task_id
• 27 bytes for the parent document's document name users/jeff
• 1 byte for the boolean field value
• 8 bytes for the integer field value
• 32 additional bytes

Collection group scope

The size of an index entry in a composite index with collection group scope is the sum of:

• The document name size of the indexed document
• The sum of the indexed field values
• 32 additional bytes

Consider a document in the sub-collection users/jeff/tasks with a string document ID of my_task_id :

- "type": "Personal"
 - "done": false
 - "priority": 1
 - "description": "Learn Cloud Firestore"

For a composite index with collection group scope that indexes the done and priority fields (both ascending), the total size of the index entry in this index is 85 bytes:

• 44 bytes for the document name users/jeff/tasks/my_task_id
• 1 byte for the boolean field value
• 8 bytes for the integer field value
• 32 additional bytes

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