Simple SQL query to find the size of tables in a database

SELECT DISTINCT
st.name
, SUM (total_pages)*8.0/1024.0 AS [Size in MB]
FROM sys.partitions sp
INNER JOIN sys.tables st
ON sp.object_id = st.object_id
INNER JOIN sys.allocation_units sa
ON sp.partition_id = sa.container_id
GROUP BY st.name