By eating a cup of popcorn only, you will be able to stay in Ketosis day in and day out. (1) You should not feel bad if you are craving this snack. But, if you are starting to eat more than a cup, you should run away. At this point, you may fall out of Ketosis. Going to the local movie theater can really put you over the edge. With the weight of popcorn bucket ranging from theater to theater, small popcorns are between 5-6 cups. (1) This is more than enough for you. So, either you can take some home for later or discard the rest of the popcorn on your way out. Unfortunately, because of the influx of measurements, grams per cup at a movie theater is between 4.5 to 6.2. (1)