Look for the symbol that resembles "|:" on the bottom left corner of a check. Be sure that you're looking at a check and not a deposit slip, which are sometimes included in the back of a checkbook.
Look to the right of the "|:" symbol. There will be a string of nine digits. That is the routing or transit number. At the end of the string of digits will be another "|:" symbol to let you know that the routing number is finished.
Look along the bottom of the check if the nine-digit number is not in the left corner. Some banks print the number in the middle of the bottom. It will always be between two "|:" symbols.