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# $count (aggregation stage)

## Definition

Passes a document to the next stage that contains a count of the number of documents input to the stage.

**Note: Disambiguation**

This page describes the `$count` aggregation pipeline stage. For the `$count` aggregation accumulator, see [`$count (aggregation accumulator)`.](https://www.mongodb.com/docs/manual/reference/operator/aggregation/count-accumulator.md#mongodb-group-grp.-count)

## Compatibility

You can use `$count` for deployments hosted in the following environments:

- [MongoDB Atlas](https://www.mongodb.com/docs/atlas): The fully managed service for MongoDB deployments in the cloud

* [MongoDB Enterprise](https://www.mongodb.com/docs/manual/administration/install-enterprise.md#std-label-install-mdb-enterprise): The subscription-based, self-managed version of MongoDB

* [MongoDB Community](https://www.mongodb.com/docs/manual/administration/install-community.md#std-label-install-mdb-community-edition): The source-available, free-to-use, and self-managed version of MongoDB

## Syntax

[`$count`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/count.md#mongodb-pipeline-pipe.-count) has the following syntax:

```javascript
{ $count: <string> }
```

`<string>` is the name of the output field which has the count as its value. `<string>` must be a non-empty string, must not start with `$` and must not contain the `.` character.

## Behavior

The return type is represented by the smallest type that can store the final value of count: [`integer`](https://www.mongodb.com/docs/manual/reference/mongodb-extended-json.md#mongodb-bsontype-Int32) → [`long`](https://www.mongodb.com/docs/manual/reference/mongodb-extended-json.md#mongodb-bsontype-Int64) → [`double`](https://www.mongodb.com/docs/manual/reference/mongodb-extended-json.md#mongodb-bsontype-Double)

The [`$count`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/count.md#mongodb-pipeline-pipe.-count) stage is equivalent to the following [`$group`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/group.md#mongodb-pipeline-pipe.-group) and [`$project`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/project.md#mongodb-pipeline-pipe.-project) sequence:

```javascript
db.collection.aggregate( [
   { $group: { _id: null, myCount: { $sum: 1 } } },
   { $project: { _id: 0 } }
] )
```

`myCount` is the output field that stores the count. You can specify another name for the output field.

If the input dataset is empty, `$count` doesn't return a result.

**See also:**

[`db.collection.countDocuments()`](https://www.mongodb.com/docs/manual/reference/method/db.collection.countDocuments.md#mongodb-method-db.collection.countDocuments) wraps the [`$group`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/group.md#mongodb-pipeline-pipe.-group) aggregation stage with a [`$sum`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/sum.md#mongodb-group-grp.-sum) expression.

## Examples

### MongoDB Shell

The examples on this page use data from the [sample\_mflix sample dataset](https://www.mongodb.com/docs/manual/sample-data/sample-mflix.md#std-label-sample-mflix). For details on how to load this dataset into your self-managed MongoDB deployment, see [Load the sample dataset](https://www.mongodb.com/docs/manual/sample-data/load-sample-data-local.md#std-label-sample-dataset-local). If you made any modifications to the sample databases, you may need to drop and recreate the databases to run the examples on this page.

The following aggregation operation has two stages:

1. The [`$match`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/match.md#mongodb-pipeline-pipe.-match) stage filters for documents where `metacritic` equals `100` to pass along only those documents to the next stage.

2. The `$count` stage returns a count of the remaining documents in the aggregation pipeline and assigns the value to a field called `perfect_score_count`.

```javascript
db.movies.aggregate( [
   { $match: { metacritic: { $eq: 100 } } },
   { $count: "perfect_score_count" }
] )

```

**Output:**

```javascript
[ { perfect_score_count: 8 } ]

```

## Learn More

- [`db.collection.countDocuments()`](https://www.mongodb.com/docs/manual/reference/method/db.collection.countDocuments.md#mongodb-method-db.collection.countDocuments)

- [`$collStats`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/collStats.md#mongodb-pipeline-pipe.-collStats)

- [`db.collection.estimatedDocumentCount()`](https://www.mongodb.com/docs/manual/reference/method/db.collection.estimatedDocumentCount.md#mongodb-method-db.collection.estimatedDocumentCount)

- [`count`](https://www.mongodb.com/docs/manual/reference/command/count.md#mongodb-dbcommand-dbcmd.count)

- [`db.collection.count()`](https://www.mongodb.com/docs/manual/reference/method/db.collection.count.md#mongodb-method-db.collection.count)