Hi Ginny,
Did you see both of your Schnoodle's parents? If so, this would be the easiest way of judging how big your Schnoodle will be, as your pup will be a size in between the 2 parents.
If you didn't see the 2 parents do you know what size or breed of Schnauzer/Poodle they both were? Again, this will give you a good idea of how big yours will grow.
If the answer to both of the above is NO, then take a look at his or her paws! If your Schnoodle has big paws, he will grow into a big Schnoodle - and vice versa! Have you got a picture you could send us?