I get this question alot.
The most simple way is to access your SQL manangement studio and look at the properties of the DB or using powershell just copy and paste the code.
SQL manangement Studio
More fun way is to learn more about powershell
First we list the DB, then sort and calculate size in MB, add better label and finally sort my name. Enjoy
Get-spdatabase
Get-spdatabase | sort-object disksizerequired | Format-Table name,disksizerequired
Get-spdatabase | sort-object disksizerequired | Format-Table name,{$_.disksizerequired/1024/1024}
Get-spdatabase | sort-object disksizerequired | Format-Table name, @{label = "Size in MB"; Expression = {$_.disksizerequired/1024/1024}}
Get-spdatabase | sort-object name | Format-Table name, @{label = "Size in MB"; Expression = {$_.disksizerequired/1024/1024}}
References
http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=193
