User IDs are your own unique identifiers that you assign to individual users. This guide explains how to send user IDs to Google Analytics, so you can connect user behavior across different sessions, devices, and platforms.
To learn more about the User-ID feature, see Measure activity across platforms. To learn how to set a user ID for an app, see Set a user ID.
Setting custom dimensions based on user IDs leads to dimensions with too many unique values. Having too many unique values causes issues with Google Analytics data and reporting accuracy. Learn more about best practices for setting custom dimensions.
Before you begin
Before you can send user IDs, make sure you've completed the following:
- Create a Google Analytics account and property.
- Create a web data stream for your website.
- Have the Editor role (or above) to the Google Analytics account.
Send user IDs
The value you send for user_id depends on the state of
the user:
- User has never signed in: Don't send the
user_idparameter. - User is signed-in: Send their user ID.
- User was signed-in, then signed out: Send
null.