You could use Storable, just freeze the structure in memory and print its length, i.e.

use Storable;

my %a = (
'a' => 'something..',
'b' => 'something else..',
)

print length(Storable::freeze(\%a))."\n";
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This will give you a "rough ball-park sizeof" without the memory overhead of using a module like Devel::Size :-)