Screen sizes (size of the bean) on green coffee varies by crop from year to year. We purchase from over 20 different origins and it would be impossible to track and provide current data for this on a regular basis.
The darker the roast the more it will expand for any coffee. For instance Ethiopia Yirgacheffe (Peaberry Bean) is very small, while Sumatra Ketiara (Elephant Bean) is almost twice the size. There are many bean size variations in the middle, however these are the two extremes Among the coffee beans we presently offer.
Throughout the world, the coffee fruit occasionally produces a single, rather than a double, bean. It grows to be small and round, with a tiny crevice that splits it halfway down the middle. Called peaberry, these beans are often separated from normal-shaped beans and sold as a separate grade of the same coffee.
According to coffee folklore, peaberry grades are considered superior to normal grades from the same crop, apparently on the basis that, in peaberries, the good stuff that ordinarily goes into a double bean goes into only one bean. Typically, peaberry is more buoyant and more brightly acidy, more complex in the upper aromatic ranges of the profile but somewhat lighter in body, than comparable normally shaped beans.
Check out this image comparison size of these beans
Maragogipe (Elephant Beans):
Maragogipe (also called elephant bean) is a variety of arabica that produces an extremely large, rather porous bean. It is a mutant that spontaneously appeared in Brazil, almost as though the giant of Latin-America thought regular beans were too puny and produced something in its own image. It was first discovered growing near the town of Maragogipe, in the northeastern state of Bahia. Subsequently it has been carried elsewhere in Latin America and generally adopts the flavor characteristics of the soil to which it has been transplanted.
Maragogipe Beans produce a thinner and less acidy cup than other traditional arabica varieties grown under the same conditions. Most Maragogipes sold in North America are grown in Mexico, Sumatra, Nicaragua, or Guatemala. Those from Chiapas, Mexico, Sumatra, and the Coban district of Guatemala have the best reputation.
References: The Coffee Review