Problem: Often we would like to check how much size backup file will take on the disk? You can follow below simple steps to estimate the backup file size?
Execute the SP_SPACEUSED procedure to get the database size statistics.
EXEC sp_spaceused @updateusage = ‘true’
Now you have to subtract the ununsed pages from reserved pages and divided by 1024 to get the output in MB.
In our scenario we have 2592 (KB) – 96 (KB) = 2496/1024 = 2.4374(MB) will be the backup size.