How to estimate the next backup size?
When we want to estimate the next backup size we can use the following stored procedure which gives some information about the backup size. The reserved column value approximately gives information about size of uncompressed backup size.
EXEC sp_spaceused @updateusage = 'true'
Reserved column defines the database size which consists of data and log files. Unused column defines a specific part of reserved data but it is not yet used by database. According to these details, we can calculate the backup size with the following formula;
Backup Size (MB) = ((Reserved (KB) – Unused (KB))/1024)/1024
For our scenario, the estimation of backup size is approximately equal to ((543328 (KB)) – (21512 (KB))/1024)/1024 = 509 (MB).This calculation method is very useful for calculating next backup size but the disadvantage of this calculation method is that it does not give any idea about the backup file growing trend or acceleration for a particular term.