The `cardinality` metric is a single-value metric aggregation that counts the number of unique or distinct values of a field.
The following example finds the number of unique products in an eCommerce store:
```json
GET opensearch_dashboards_sample_data_ecommerce/_search
{
"size": 0,
"aggs": {
"unique_products": {
"cardinality": {
"field": "products.product_id"
}
}
}
}
```
{% include copy-curl.html %}
#### Example response
```json
...
"aggregations" : {
"unique_products" : {
"value" : 7033
}
}
}
```
Cardinality count is approximate.
If you have tens of thousands of products in your hypothetical store, an accurate cardinality calculation requires loading all the values into a hash set and returning its size. This approach doesn't scale well; it requires huge amounts of memory and can cause high latencies.
You can control the trade-off between memory and accuracy with the `precision_threshold` setting. This setting defines the threshold below which counts are expected to be close to accurate. Above this value, counts might become a bit less accurate. The default value of `precision_threshold` is 3,000. The maximum supported value is 40,000.
```json
GET opensearch_dashboards_sample_data_ecommerce/_search
