Sizing database/partition/partitioned table with [dm_db_partition_stats]

--
-- whole database size
SELECT   
        (SUM(reserved_page_count)*8192)/1024000 AS [TotalSpace(MB)]
        ,(SUM([used_page_count])*8192)/1024000 AS [UsedSpace(MB)]
        ,(SUM([row_count])) AS [RowCount]
        FROM sys.dm_db_partition_stats

--
-- size of each partition scheme       
select    s.name as [partition_scheme]
        ,sum(ps.[reserved_page_count])*8192/10240000  AS [TotalSpace(MB)]
        ,sum(ps.[used_page_count])*8192/10240000 AS [UsedSpace(MB)]
        ,sum([row_count]) AS [RowCount]
    from    sys.indexes i inner join sys.partition_schemes s
            on i.data_space_id = s.data_space_id 
            inner join
                (
                SELECT   
                    [object_id]
                    ,[index_id]
                    ,sum([used_page_count]) as [used_page_count]
                    ,sum([reserved_page_count]) as [reserved_page_count]
                    ,sum([row_count]) as [row_count]
                    FROM [sys].[dm_db_partition_stats]
                    group by [object_id],[index_id]
                ) ps
            on ps.object_id=i.object_id and ps.index_id=i.index_id
    group by s.name
    order by 1,2

--
-- size of partitioned table
select
        object_schema_name(i.object_id) as [schema]
        ,object_name(i.object_id) as [object]
        ,i.name as [index]
        ,ps.[used_page_count]
        ,ps.[reserved_page_count]
        ,ps.[row_count]
        ,s.name as [partition_scheme]
        ,f.name as [patition_function]
    from    sys.indexes i inner join sys.partition_schemes s
            on i.data_space_id = s.data_space_id 
            inner join sys.partition_functions f
            on f.function_id = s.function_id
            inner join
                (
                SELECT   
                    [object_id]
                    ,[index_id]
                    ,sum([used_page_count]) as [used_page_count]
                    ,sum([reserved_page_count]) as [reserved_page_count]
                    ,sum([row_count]) as [row_count]
                    FROM [sys].[dm_db_partition_stats]
                    group by [object_id],[index_id]
                ) ps
            on ps.object_id=i.object_id and ps.index_id=i.index_id
    order by 1,2,3