How to find the Routing Number?

Short answer is you cannot.

Even if you did, routing number will not work without the bank account number, and the bank account number is not the same as what you see on the debit card.

Closest you can get is this: The first 6 digits of the debit card will give you the financial institution that issued the debit card. If that financial institution has only one routing number for the entire US, there you go, you have the routing number. But this is an exception.

Many major banks have multiple routing numbers based on the state that the bank account was initially opened. If the bank that issued the debit card is one of them you will have a list of possible routing numbers but not a specific one.

The current billing zip code may hint in which state the account was opened. However, if the account owner moved to another state after opening the account since the routing number will not change, the billing zip code will not lead you to the right routing number.