my $s="\x{5fcd}\x{65e0}\x{53ef}\x{5fcd}";
use Encode;
print length encode("utf8", $s), "\n"; # 12

##</code><code>##

print do {use bytes; length($s)}, "\n"; # 12 (see perldoc -f length)

# or

utf8::encode($s); # resets the utf8 flag
print length($s), "\n"; # 12