如何计算Oracle中的表大小

Being used to (and potentially spoiled by) MSSQL, I'm wondering how I can get at tables size in Oracle 10g. I have googled it so I'm now aware that I may not have as easy an option as sp_spaceused. Still the potential answers I got are most of the time outdated or don't work. Probably because I'm no DBA on the schema I'm working with.Being used to (and potentially spoiled by) MSSQ