Annette,
You didn't say how large you wanted your finished block but the answer is always the same. If want your finished block to be 9" for example: divide that size by 3 that gives you the size of each square within your 9patch. Then add 1/2" for seam allowances. That is 1/4" on each side. So a 9" nine patch will take strips of 3 1/2" fabric to complete. I'm assuming here that you plan to strip piece your project. Hope I answered your question.