Oracle extents - How can I have so few with this large size?
You may believe that this is a different question but my answer is going to be essentially identical assuming the additional information from the prior question is the same-- you're using automatic extent allocation and you're not sure how Toad is determining these numbers.

The data you're getting from Toad appears to be incorrect or, at least, misleading.  If you are using a locally managed tablespace with automatic extent allocation, Oracle will determine your initial and next extent sizes automatically.  In 11.2, the first 16 extents are going to be 64k in size (for a total of 1 MB).  The next 63 extents are going to be 1 MB in size.  So if you have 12 extents, that implies that the table occupies 768 kb of space on disk.  An initial extent of 118 MB makes no sense and a size of 376 MB makes no sense.

What does

SELECT tablespace_name,
       extent_id, 
       bytes/1024 kb
  FROM user_extents
 WHERE segment_name = &lt;&lt;name of index&gt;&gt;


show you?  If you have 12 extents, you should see that extents 0-11 are 64 kb in size.

SELECT SUM(bytes)/1024/1024 size_in_mb
  FROM user_extents
 WHERE segment_name = &lt;&lt;name of index&gt;&gt;


will show you the total size of the table's extents on disk.