How to determine the size of tables in sql server?

For single size of tables in sql server you can use

sp_spaceused MyTable

For all tables in a database you can use it with sp_msforeachtable as following

CREATE TABLE #temp (

table_name sysname ,
row_count INT,
reserved_size VARCHAR(50),
data_size VARCHAR(50),
index_size VARCHAR(50),
unused_size VARCHAR(50))

SET NOCOUNT ON

INSERT #temp

EXEC sp_msforeachtable 'sp_spaceused ''?'''
SELECT a.table_name,
a.row_count,
COUNT(*) AS col_count,
a.data_size

FROM #temp a

INNER JOIN information_schema.columns b
ON a.table_name collate database_default
= b.table_name collate database_default
GROUP BY a.table_name, a.row_count, a.data_size
ORDER BY CAST(REPLACE(a.data_size, ' KB', '') AS integer) DESC

DROP TABLE #temp