Below query will give you exact size of data stored in Table:
CREATE TABLE #Size ( [TableName] VARCHAR(100) ,[TotalBytes] INT ) SELECT ROW_NUMBER() OVER(ORDER BY CONCAT(C.TABLE_SCHEMA,C.TABLE_NAME)) [RNo] ,CONCAT('SELECT ''[',C.TABLE_SCHEMA,'].[',C.TABLE_NAME,']'' [TableName], ', STRING_AGG(CONCAT('ISNULL(SUM(DATALENGTH(',[COLUMN_NAME],')),0)'), ' + '), ' [TotalBytes] FROM [', C.TABLE_SCHEMA, '].[', C.TABLE_NAME,']') [Query] INTO #Queries FROM Information_Schema.COLUMNS C LEFT JOIN Information_Schema.VIEW_TABLE_USAGE V ON C.TABLE_NAME = v.VIEW_NAME WHERE V.VIEW_NAME IS NULL GROUP BY C.TABLE_SCHEMA, C.TABLE_NAME DECLARE @sqlcmd VARCHAR(MAX) = (SELECT STRING_AGG(Query,';' + CHAR(10)) FROM #Queries) INSERT INTO #Size EXEC(@sqlcmd); SELECT * FROM #Size

In MS SQL If you want to get exact size of data stored in all tables then you can get it like this:
CREATE TABLE #Size ( [TableName] VARCHAR(100) ,[TotalBytes] INT ) SELECT ROW_NUMBER() OVER(ORDER BY CONCAT(C.TABLE_SCHEMA,C.TABLE_NAME)) [RNo] ,CONCAT('SELECT ''[',C.TABLE_SCHEMA,'].[',C.TABLE_NAME,']'' [TableName], ', STRING_AGG(CONCAT('ISNULL(SUM(DATALENGTH(',[COLUMN_NAME],')),0)'), ' + '), ' [TotalBytes] FROM [', C.TABLE_SCHEMA, '].[', C.TABLE_NAME,']') [Query] INTO #Queries FROM Information_Schema.COLUMNS C LEFT JOIN Information_Schema.VIEW_TABLE_USAGE V ON C.TABLE_NAME = v.VIEW_NAME WHERE V.VIEW_NAME IS NULL GROUP BY C.TABLE_SCHEMA, C.TABLE_NAME DECLARE @sqlcmd VARCHAR(MAX) = (SELECT STRING_AGG(Query,';' + CHAR(10)) FROM #Queries) INSERT INTO #Size EXEC(@sqlcmd); SELECT * FROM #Size