Below is a ready-to-use script. Review and adapt variables to your environment.
-- Run in master
SELECT
DB_NAME(database_id) AS [Database],
CAST((SUM(total_page_count)*8.0)/1024 AS DECIMAL(10,2)) AS [SizeMB]
FROM sys.dm_db_file_space_usage
GROUP BY database_id
ORDER BY [SizeMB] DESC;