Firestore errorFirestore: document exceeds the maximum size (1 MiB)

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Why the document is too large, and the fix

1. 01

   A file is stored in the document

   “Maximum size for a document 1 MiB (1,048,576 bytes)” Firebase, Usage and limits

   Base64 makes a file about a third bigger, so a photo of under 1 MB can still break the limit. Upload the file to Cloud Storage and save its path in the document.

2. 02

   A list keeps growing in one document

   Chat messages, comments or logs added with arrayUnion grow until the writes start failing. Store each item as its own document in a subcollection, and add security rules for the new path.

   // one document per message, not one growing array
   await addDoc(collection(db, 'chats', chatId, 'messages'), {
     text,
     senderId: user.uid,
     createdAt: serverTimestamp(),
   });

3. 03

   Several big fields add up

   “For example, four fields of 256 KiB each exceed the limit.” Google Cloud, Error codes (INVALID_ARGUMENT)

   The limit applies to the whole document, so fields that are fine on their own can be too much together. Split them into separate documents.

4. 04

   Text is counted in bytes, not characters

   “String sizes are calculated as the number of UTF-8 encoded bytes + 1.” Firebase, Storage size calculations

   Field names and string values are counted as UTF-8 bytes, so emoji and non-Latin text use more space than they look. Long field names in big maps add up too.

Checked against the vendor’s docs on November 9, 2026: Firebase docs: Usage and limits; Google Cloud docs: Firestore error codes; Firebase docs: Storage size calculations.

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Related: Firestore transaction too big · Firestore quota exceeded · Firestore in query limit (30) · Firestore ALREADY_EXISTS