El siguiente script en TSQL lista todas las bases de datos con sus respectivos tamaños en Megas y Gigas.

SELECT DB_NAME(db.database_id) DatabaseName,
round((CAST(mfrows.RowSize AS FLOAT)*8)/1024,2) RowSizeMB,
round((CAST(mflog.LogSize AS  FLOAT)*8)/1024,2) LogSizeMB,
round((CAST(mfrows.RowSize AS FLOAT)*8)/1024+(CAST(mflog.LogSize AS FLOAT)*8)/1024,2) DBSizeMB,
round((CAST(mfrows.RowSize AS FLOAT)*8)/1024/1024+(CAST(mflog.LogSize AS FLOAT)*8)/1024/1024,2) DBSizeGB
FROM sys.databases db LEFT JOIN
(SELECT database_id, SUM(size) RowSize FROM sys.master_files WHERE type = 0
  GROUP BY database_id, type) mfrows
ON mfrows.database_id = db.database_id LEFT JOIN
(SELECT database_id, SUM(size) LogSize FROM sys.master_files WHERE type = 1
  GROUP BY database_id, type) mflog
ON mflog.database_id = db.database_id LEFT JOIN
(SELECT database_id,SUM(size) StreamSize FROM sys.master_files WHERE type = 2
 GROUP BY database_id, type) mfstream
ON mfstream.database_id = db.database_id LEFT JOIN
(SELECT database_id, SUM(size) TextIndexSize FROM sys.master_files  WHERE type = 4
  GROUP BY database_id, type) mftext
ON mftext.database_id = db.database_id
ORDER BY 4 DESC

Complementa al siguiente script para listar las bases de datos con su ubicación:
https://maurobernal.com.ar/blog/t-sql/listar-todas-las-bases-de-datos-con-su-respectiva-ubicacion-y-tamanos/