If your spice rack doesn't come with its own jars, check the dimensions of the shelves to see what size jars it will take. Good spice racks should be able to accommodate the majority of jars or herbs and spices you'd find in a grocery store, though some models only fit standard-sized jars. If you know you often buy non-standard-sized jars of herbs or spices, be sure to select a spice rack that can hold them.