How many possibilities for a numerical PIN with exactly 9 digits? How about a PIN with no more than 9 digits?
For a PIN of length 9, you have exactly
10^9 = 1000000000 combinations (which can be brute-forced by a computer in less than one second). That's 29.9 bits of entropy.
For a PIN of at most 9 digits, you have exactly
10^9 + 10^8 + ... + 10^1 = 1111111110 combinations, which is not that greater than the previous answer. That's 30.0 bits of entropy.