Yes, I agree it was 64kb. I'm not sure now, though because I will be using the bitmap and not the header space.

Here is from the docs. But, doesn't say how much space for bitmap?

"Note:
When you allocate a datafile for a locally managed tablespace, you should allow space for metadata used for space management (the extent bitmap or space header segment) which are part of user space. For example, if specify the UNIFORM clause in the extent management clause but you omit the SIZE parameter, then the default extent size is 1MB. In that case, the size specified for the datafile must be larger (at least one block plus space for the bitmap) than 1MB."