The picture below demonstrates: The colorful plate (The Portion Plate) is the proper size of a plate. It is sitting on top of a plate that most of us have in our homes today. The portion plate is about 10 inches in diameter. The white plate is about 12 inches in diameter.
Studies have been done: The larger the plate, the larger the portion and yes, we eat it all. And, that means we pack on a lot more calories than we should. Next time you're at a restaurant, pay close attention to the portion sizes. They are enormous.
You might want to check out the Portion Plate site.