How to Count Documents in MongoDB: Syntax and Examples

To count documents in MongoDB, use the countDocuments() method on a collection. This method returns the number of documents matching a query filter or all documents if no filter is provided.

Syntax

The countDocuments() method counts documents in a collection that match a given filter.

• filter: An optional object to specify criteria for matching documents.
• options: Optional settings like limit or skip.

Example syntax:

db.collection.countDocuments(filter, options)

mongodb

db.collection.countDocuments({ age: { $gt: 25 } })

Example

This example counts how many users are older than 25 in the users collection.

javascript

const { MongoClient } = require('mongodb');

async function countUsers() {
  const uri = 'mongodb://localhost:27017';
  const client = new MongoClient(uri);

  try {
    await client.connect();
    const database = client.db('testdb');
    const users = database.collection('users');

    const count = await users.countDocuments({ age: { $gt: 25 } });
    console.log('Number of users older than 25:', count);
  } finally {
    await client.close();
  }
}

countUsers();

Output

Number of users older than 25: 42

Common Pitfalls

Common mistakes when counting documents include:

• Using count() instead of countDocuments(), which is deprecated and less accurate.
• Not providing a filter when you want to count specific documents.
• Confusing estimatedDocumentCount() with countDocuments(); the former is faster but less precise.

mongodb

/* Wrong: deprecated count() method */
db.users.count({ age: { $gt: 25 } });

/* Right: use countDocuments() */
db.users.countDocuments({ age: { $gt: 25 } });

Quick Reference

Method	Description	Use Case
countDocuments(filter)	Counts documents matching filter	Accurate count with query
estimatedDocumentCount()	Estimates total documents quickly	Fast count without filter
count()	Deprecated method	Avoid using

Key Takeaways

Use countDocuments() to count documents matching a filter in MongoDB.

Avoid the deprecated count() method for counting documents.

estimatedDocumentCount() is faster but less precise and does not accept filters.

Always provide a filter to countDocuments() when you want specific counts.

countDocuments() returns a promise in modern drivers, so use async/await or callbacks.