Command to get a listing of each object and it's size, the number of objects and their total size in human readable format:

aws s3 ls --summarize --human-readable --recursive s3://BUCKET_NAME/

# output is a really long listing ... with this format:
2018-02-04 20:33:31 2.2 MiB Pictures/Personal Photos/Vietnam/vietnam/2018-01-25/9890.JPG
2018-02-04 20:33:47 2.1 MiB Pictures/Personal Photos/Vietnam/vietnam/2018-01-25/9891.JPG
2018-02-04 20:33:31 2.2 MiB Pictures/Personal Photos/Vietnam/vietnam/2018-01-25/9893.JPG

Total Objects: 1699
Total Size: 5.1 GiB