How to see the number of extents

Hi,

For an index, I have the max extents set to 100. I want to know what is the current number of extents already allocated. Which table gives me this info
Badrinath

select extents from user_segments where segment_name='YOUR_INDEX_NAME'

select extents, max_extents from dba_segments where segment_name='...'

And,how do I know, What is the blocks used in the current extent.
So I can have an Idea by when I may have to increase the datafile space.
Badrinath

select segment_name, bytes, blocks from dba_extents where
segment_name='yourSEGMENT'

In case your segment is a partition, PARTITION_NAME column exist in this views. (8i only)