Checks have three sets of numbers printed on the bottom. According to the United States Patent and Trademark Office, the first nine-digit number is the routing number, and the second number is the account number.
Although this is the most common layout on checks, according to the Dallas County Community College District, these three numbers may be listed in any order.
The routing number is always nine digits long and is marked on the check with |: on either side of the number, states the United States Patent and Trademark Office. This number is assigned to the bank by the American Bankers Association, states the FDIC.
The account number is assigned to the customer by the bank. According to the Dallas County Community College District, account numbers may be up to 17 digits long. The third number is the check number and should match the number printed in the upper right hand corner of the check.