Only 6 to 8 pieces each time. I tried twice with double rack, but it was difficult to control, and the top layer ones were too brown while the bottom ones were too light. If you cover the top layer by a foil paper, it would be hot & difficult for you to check them by removing the foil paper in between the cooking time. Therefore, I recently only do one layer each time. Use 180 degree for 12-15 minutes and stay there for another 5 minutes before taking them out. I do not preheat it because it will be too hot for me to put the cookies inside the tray. Time is all depended on the thickness of your cookies and whether you put the cookies onto a baking dish instead of using the tray with the holes. The machine is good that you can take the tray out and check your food from time to time.