my $hashref = { 'key' => 'value' };

my $sum1 = 0;
$sum1 += length for %$hashref;
# - or -
my $sum2 = length join '', %$hashref;
# - or -
use List::Util qw/sum/;
my $sum3 = sum map {length} %$hashref;

##</code><code>##

my $sum4 = 0;
while ( my ($k, $v) = each %$hashref )
	{ $sum4 += length($k) + length($v) }