The solution in the article is much more detailed and I'm certainly going to try it, but if you regularly take backups and want a quick result, you can query db growth history like this (its the total dbsize, incl log and accurate as long as there's no compression involved):

select

database_name,

BackupDate = convert(varchar(10),backup_start_date, 111)

,SizeInGigs=( backup_size/1024000000)

from msdb..backupset

where

type = 'd'

order by database_name, backup_start_date desc