This will depend partially on the number of people you are cooking for and partially on the type of cooking you are doing. - For singles a 1 - 1 1/2 quart is ideal. - For a couple a 2 1/2- 3 1/2 quart is perfect. - For a family of 3 to 4 choose a 3 1/2 - 4 1/2 quart. - For families of 4 to 5 choose a 4 1/2 - 5 quart unit. - For feeding 6 or more people a 6 quart is the best option. Of course a larger size is a great choice if you want to have leftovers to freeze and serve later. Most roasts also fit better in a 5 quart or larger unit.