The average weight for a healthy adult cat is between 8 and 10 pounds, although among purebreds, what's normal can vary dramatically by breed. The Singapura, a rare breed whose lines trace to the feral cats of Singapore, is perhaps the smallest breed of cat, with some animals weighing in at less than half the weight of an average cat.

The Siberian, another rare breed, is said to be the biggest cat, with some animals topping the 20-pound mark. Other breeds that aren't quite as large but still qualify for big-cat status include the ragdoll, Turkish van, Maine coon, Norwegian forest and British shorthair.