SQL Query to get Database size infromation

SELECT Name,
[Filename],
CONVERT (Decimal(15,2),ROUND(a.Size/128.000,2)/1024) [Currently Allocated Space (GB)],
CONVERT (Decimal(15,2), ROUND(FILEPROPERTY(a.Name,'SpaceUsed')/128.000,2)/1024) AS [Space Used (GB)],
CONVERT (Decimal(15,2),ROUND((a.Size-FILEPROPERTY(a.Name,'SpaceUsed'))/128.000,2)/1024) AS [Available Space (GB)]
FROM dbo.sysfiles a (NOLOCK)
JOIN sysfilegroups b (NOLOCK) ON a.groupid = b.groupid
ORDER BY b.groupname;