We have recently added Plush Sizes to help you out, since the pictures don't always show how big an animal is.
Small: About 3-6 inches long and fits in one hand.
Medium: About 6-12 inches long and can be held in two hands
Large: About 12-16 inches long, and can be tucked under one arm.
Extra-Large: So big that you can barely hold it at all even with two arms. Some may be big enough to ride on.