result.txt

$ perl s.pl
keys:10000 size:1348738
keys:20000 size:2708562
keys:30000 size:3478562
keys:40000 size:5428210
keys:50000 size:6198210
keys:60000 size:6968210
keys:70000 size:10097506
keys:80000 size:10867506
keys:90000 size:11637506
keys:100000 size:12407507
keys:110000 size:13187507
keys:120000 size:13967507
keys:130000 size:14747507
keys:140000 size:20246099
keys:150000 size:21026099
keys:160000 size:21806099
keys:170000 size:22586099
keys:180000 size:23366099
keys:190000 size:24146099
keys:200000 size:24926099

size.pl

use 5.12.1;
use B ();
use B::Size2 ();

my $bighash = {};
for my $key ( 1 .. 200_000 ) {
    $bighash->{$key} = "foo";
    if ( $key % 10000 == 0 ) {
        say "keys:$key size:", B::svref_2object($bighash)->size;
    }
}