These are under 3 inch oyster shells but may have some smaller or larger. If smaller you will receive a few extra. They are just random picked shells. All shells have been boiled and wiped clean before shipping. These are great for different craft projects but also for Isopods or aquarium decorations. I use these in my isopods bins as a calcium supplement and they love them since they double as a hide and somewhere they can regulate humidity. They also last much longer then cuttlebone.