There are two scripts I like to use to look at the file sizes on servers.  The first one is everything I could hope for on servers where there is only a single file per filegroup.  All of the vital information is all in one place.  I know, DBAs tend to be good at math and there was no need for me to make all of these columns.  However, any room I leave to demonstrate my mathematical powers in a professional environment…. Ok, look, CPU time is cheap anymore, I’ll go with that for my reasoning.

IF Object_ID('TempDB..##FileSize') IS NOT NULL BEGIN
    DROP TABLE ##FileSize
END

CREATE TABLE ##FileSize
(      DB VarChar(128)
    , FileLogicalName VarChar(128)
    , FilePhysicalName VarChar(512)
    , FileGroup VarChar(128)
    , Used_MB VarChar(128)
    , Free_MB VarChar(128)
    , Size_MB VarChar(128)
    , GrowthRate VarChar(128)
    , MaxSize VarChar(128)
)

exec sp_MSforeachdb N'use [?]; 
INSERT INTO ##FileSize
SELECT DB = db_name()
    , FileLogicalName = f.name
    , FilePhysicalName = f.physical_name
    , FileGroup = ISNULL(g.name, f.Type_Desc) 
    , Used_MB = REPLACE(CONVERT(varchar(100), (CAST((FileProperty(f.name, ''SpaceUsed'')) / 128 AS money)), 1), ''.00'', '''')
    , Free_MB = REPLACE(CONVERT(varchar(100), (CAST((f.size - FileProperty(f.name, ''SpaceUsed'')) / 128 AS money)), 1), ''.00'', '''')
    , Size_MB = REPLACE(CONVERT(varchar(100), (CAST((f.size) / 128 AS money)), 1), ''.00'', '''')
    , GrowthRate = Case Is_Percent_Growth
                    WHEN 1 THEN '''' + Cast(Growth as VarChar(100)) + ''%''
                    ELSE REPLACE(CONVERT(varchar(100), (CAST(Growth/128 AS money)), 1), ''.00'', '''') + '' MB''
                    END 
    , MaxSize = Case Max_Size
                    WHEN -1 THEN ''---''
                    WHEN 268435456 THEN ''---''
                    ELSE REPLACE(CONVERT(varchar(100), (CAST(Max_Size/128 AS money)), 1), ''.00'', '''') + '' MB''
                    END
FROM sys.database_files f
    LEFT JOIN sys.filegroups g on f.data_space_id = g.data_space_id
'

SELECT *
    , PctUsed = Cast(100 * replace(Used_MB, ',', '') / (Cast(replace(Size_MB,',', '') as Dec(20,2)) + .01) as Dec(20,2))
    --, PctFree = 100 - Cast(100 * replace(Used_MB, ',', '') / (Cast(replace(Size_MB,',', '') as Dec(20,2)) + .01) as Dec(20,2))
FROM ##FileSize
--WHERE DB = 'msdb'
ORDER BY FilePhysicalName

DROP TABLE ##FileSize

The problem with that script is that there are times it makes sense to have multiple files in a filegroup.  Be it disk limitations, best practices on a SAN saying not to extend a LUN, or your predecessor tossed logic to the wind, there are many reasons you could have multiple files where the previous script leaves you doing math to figure out how big the filegroup is or how much room for growth you have.  You know what I said about doing math…CPU time is cheap.  Here’s what I use when I need to see the filegroup sizes.

IF Object_ID('TempDB..##FileGroupSize') IS NOT NULL BEGIN
    DROP TABLE ##FileGroupSize
END

CREATE TABLE ##FileGroupSize
(      DB VarChar(128)
    , FileGroup VarChar(128)
    , Used_MB Int
    , Free_MB Int
    , Size_MB Int
)

exec sp_MSforeachdb N'use [?]; 
INSERT INTO ##FileGroupSize
SELECT DB = db_name()
    , FileGroup = ISNULL(g.name, f.Type_Desc) 
    , Used_MB = SUM(FileProperty(f.name, ''SpaceUsed'')) / 128
    , Free_MB = SUM(f.size - FileProperty(f.name, ''SpaceUsed'')) / 128
    , Size_MB = SUM(f.size) / 128 
FROM sys.database_files f
    LEFT JOIN sys.filegroups g on f.data_space_id = g.data_space_id
GROUP BY f.Type_Desc, g.name
'

SELECT *
    , PctUsed = Cast(100 * Used_MB / (Cast(Size_MB as Dec(20,2)) + .01) as Dec(20,2))
    , PctFree = 100 - Cast(100 * Used_MB / (Cast(Size_MB as Dec(20,2)) + .01) as Dec(20,2))
FROM ##FileGroupSize
ORDER BY DB, FileGroup

DROP TABLE ##FileGroupSize

It should be noted that I have different rules for different situations.  If a script is part of a stored proc or view then * isn’t even a consideration.  If an external program, even an SSRS report, will consume the code then I would never try to format it using SQL.  However, these are saved in my scripts folder as FileSize.sql and FilegroupSizes.sql, and my personal .sql files get to break a rule or two.