SQL Server - Get filegroup and files space details

SELECT
b.groupname AS 'File Group',
Name,
[Filename],
CONVERT (Decimal(15,2),ROUND(a.Size/128.000,2))
[Currently Allocated Space (MB)],
CONVERT (Decimal(15,2),
ROUND(FILEPROPERTY(a.Name,'SpaceUsed')/128.000,2))
AS [Space Used (MB)],
CONVERT (Decimal(15,2),
ROUND((a.Size-FILEPROPERTY(a.Name,'SpaceUsed'))/128.000,2))
AS [Available Space (MB)]
FROM dbo.sysfiles a (NOLOCK)
JOIN sysfilegroups b (NOLOCK) ON a.groupid = b.groupid
ORDER BY b.groupname