A 6-quart Instant Pot is ideal for cooking a standard rack of baby back ribs (up to 5 pounds). If you have a larger Instant Pot or pressure cooker, such as a 12-quart size, you can cook multiple racks simultaneously. Note: if cooking multiple racks at once, there is no need to adjust the cooking time. The pressure cooker will naturally adjust the time it takes to come to pressure, eliminating your need to do so. However, I would double the amount of liquid added to the pot.