Is it possible to display the size of individual buckets?

It is not possible to display the size of all objects in a bucket in the administration interface.

If you have installed and configured the command line tool s3cmd (see article), you can calculate the size as follows:

$ s3cmd du -H s3://example/
  10G               3 objects s3://example/
$ s3cmd du s3://example/
  10739648901       3 objects s3://example/

Other tools that interact with the S3 API may offer comparable functionality.

Tip: The memory consumption of all your buckets can be checked in the Analytics tab under "Storage bytes".