What they do. Custom parameters on an item-level grant you the opportunity to gather more data about products on your website or app, extending beyond the standard parameters provided by default. For instance, item-specific custom parameters can be employed to obtain information about a product’s color, size, customer rating, and availability status.

How it works. When establishing a custom dimension or metric, you need to supply the name of the custom event parameter or custom user property that Analytics will link to the new dimension or metric. Subsequently, Analytics fills the newly created dimension or metric with values gathered from the respective event parameter or user property.

Best practices. Prior to creating custom dimensions and metrics, Google recommends utilizing the default dimensions and metrics.

For advertisers with a standard property, refrain from generating excessive high-cardinality custom dimensions, as they can adversely affect your reports and lead to data aggregation under the (other) row.

Additionally, it is not considered best practice to register a custom dimension for a parameter already defined as a dimension, such as page and screen dimensions or transaction ID. While this won’t influence cardinality, it will consume part of your custom dimension quota.

Limits. Google suggests that if you reach the following limits, to archive the ones you do not use and create new ones.

Dig deeper. To learn how to archive or set up custom dimensions, visit the Analytics Help guide.

Why we care. Custom dimensions and metrics provide valuable insights that can enhance ad campaign performance, improve targeting, and ultimately boost return on investment (ROI).