A stock pot is designed to heat liquids rapidly and then simmer and evenly heat them for long periods of time. Dutch ovens, much heavier and thicker than stock pots, are often made of cast iron and designed to braise foods over open flames.
Although a Dutch oven can make soups, and stock pots can be used for braising, each is designed to cook different types of meals. Because it’s easier and more economical to make soups in large batches, stock pots have evolved to simmer several quarts of soups and stock. Because soups and stocks are mostly liquid, stock pots can be thinner and lighter so that the pan comes to cooking temperature quickly. Stock pots can also simmer at relatively low temperatures for a long time. This improves the quality of soups and stocks because ingredients have sufficient cooking time to diffuse and incorporate.
Dutch ovens, however, are big heavy pots designed to protect food from scorching flames. Because meals traditionally cooked in them are heavy, such as stews, casseroles, braised meats and vegetables, and cook for very long periods, cast-iron Dutch ovens retain even heat while their tight-fitting lids retain moisture so that food finishes juicy and tender. Unlike stock pots, Dutch ovens can be used to cook over open fires or heated in the oven to save space.