use Devel::Size qw/total_size/;

$h{$_} = 1 for "aaaaa".."zzzzz";
$elements_size += total_size $_ for %h;
$hash_size = total_size \%h;
print <<INFO;
Total size of the contained elements: $elements_size
Total size of the hash:               $hash_size
INFO
__DATA__
Total size of the contained elements: 1223781728
Total size of the hash:               1167897536