> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getlago.com/llms.txt
> Use this file to discover all available pages before exploring further.

# UNIQUE COUNT

The unique count aggregation type counts only the unique values of a specified event property.

<Frame caption="UNIQUE COUNT calculation method">
  <img src="https://mintcdn.com/lago/L7Dc2Fm9iHz3bRSl/guide/images/count-unique.png?fit=max&auto=format&n=L7Dc2Fm9iHz3bRSl&q=85&s=df1fa7778bb5858841756fd460598a6d" width="3840" height="2160" data-path="guide/images/count-unique.png" />
</Frame>

## UNIQUE COUNT billable metric

<Tabs>
  <Tab title="Dashboard">
    Here is how you can create a unique count aggregation from the UI:

    1. Access the **"Billable metrics"** section via the side menu;
    2. Create a new billable metric;
    3. Define a name, a code and an optional description;
    4. Select **"count unique"** as the aggregation type;
    5. Define if this metric is `metered` or `recurring`;
    6. Define the property to aggregate;
    7. Apply dimension groups if any; and
    8. Click **"Add billable metric"**.

    <Info>
      This billable metric can be both `metered` or `recurring`.
    </Info>
  </Tab>

  <Tab title="API">
    <CodeGroup>
      ```bash theme={"dark"}
          LAGO_URL="https://api.getlago.com"
          API_KEY="__YOUR_API_KEY__"

          curl --location --request POST "$LAGO_URL/api/v1/billable_metrics" \
          --header "Authorization: Bearer $API_KEY" \
          --header 'Content-Type: application/json' \
          --data-raw '{
              "billable_metric": {
              "name": "API Request",
              "code": "api_requests",
              "description": "Number of API requests.",
              "aggregation_type": "unique_count_agg",
              "field_name": "request_id",
              "group": {}
          }
      }'
      ```
    </CodeGroup>
  </Tab>
</Tabs>

## Calculation example

Lago calculates the `COUNT_DISTINCT(events.properties.property_name)` for the two following events received.

```json theme={"dark"}
//Event received #1
{
    "transaction_id": "transaction_1",
    "external_customer_id": "1",
    "timestamp": "2022-03-16T00:00:00Z",
    "code": "api_requests",
    "properties": {
        "request_id": "id_1"
    }
}

//Event received #2
{
    "transaction_id": "transaction_2",
    "external_customer_id": "1",
    "timestamp": "2022-03-17T00:00:00Z",
    "code": "api_requests",
    "properties": {
        "request_id": "id_1"
    }
}
```

In that case, with this aggregation type, Lago only counts the unique values of the `request_id` property in the event payloads, **resulting in a billable value of 1 unit.**