If you have an array @a, using it in a scalar context gets the number of elements:

my @a = ( 3, 1, 4, 1, 5 );
my $N = @a;
say $N; # or print "$N\n; before 5.10
my $aref = \@a;
$refsize = @$aref; # or @{$aref};
say $refsize;
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For a multidimensional array, you wind up with a reference to the inner array, so use the ref example:

my @twoD = ( [ 1, 2, 3 ],
             [ 4, 5, 6 ],
           );
print "Top level or array has " . scalar @twoD . " elements\n";
for my $row ( @twoD ) {
   print "row has " . scalar @$row . " elements\n";
}
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