Query below returns tables in a database with space they use ordered from the ones using most.

Query

select schema_name(tab.schema_id) + '.' + tab.name as [table], 
    cast(sum(spc.used_pages * 8)/1024.00 as numeric(36, 2)) as used_mb,
    cast(sum(spc.total_pages * 8)/1024.00 as numeric(36, 2)) as allocated_mb
from sys.tables tab
    inner join sys.indexes ind 
        on tab.object_id = ind.object_id
    inner join sys.partitions part 
        on ind.object_id = part.object_id and ind.index_id = part.index_id
    inner join sys.allocation_units spc
        on part.partition_id = spc.container_id
group by schema_name(tab.schema_id) + '.' + tab.name
order by sum(spc.used_pages) desc

Columns

• table - table name with schema name
• used_mb - space used in MB
• allocated_mb - space allocated in MB

Rows

• One row represents one table in a database
• Scope of rows: all tables in a database
• Ordered by table used size, from largest to smallest

Sample results

Tables in AdventureWorks ordered from the ones using most space to least.