To get recent size of all databases on an instance

SELECT d.name,
ROUND(SUM(mf.size) * 8 / 1024, 0) Size_MBs
FROM sys.master_files mf
INNER JOIN sys.databases d ON d.database_id = mf.database_id
WHERE d.database_id > 4 — Skip system databases
GROUP BY d.name
ORDER BY d.name