Every slow cooker is different, so you may use a little less or a little more tortillas, depending on how yours "stacks" up. We used a rectangular, casserole-style (13x9) slow cooker for testing purposes, and we used 18 corn tortillas (3 layers of 6 each). A conventional, oval slow cooker might use 4 layers of 4, for example, while a round one might use even less.