Using the Capacity page in the Power Platform Admin Center we can extract the details of size occupied by table (in MB) within a particular environment.
Login to the admin portal and navigate to Capacity
Select the Dataverse tab and click on Details or in case of trial click on the Trial tab
Here we have selected the details (graph) option for one of the environments.
Select Download all tables option for the Top database capacity use, by table chart
We can see the details within the extracted CSV file.
Get all the details here
Hope it helps..