I produce three period correct sizes in tintypes:
1/6 plate
1/4 plate
1/2 plate
Half Plate 4 1/4 x 5 1/2 inches. This is the largest plate size that I can create. It is a nice big plate, and allows for a lot of detail and accommodates large groups in the photograph.
Sixth Plate: 2 3/4 x 3 1/4 inches. This size is perfect for seated or standing portraits, or small group photographs. It is the same size as most of the period and reproduction "Union" cases available at reenactments, antique stores and online auctions. This was also the size most soldiers would mail home to their families after their image was "struck" by a photographer in the field.
Quarter Plate: 3 1/4 x 4 1/4 inches. This is a very popular plate size. The image is larger than the sixth plate, allowing for a more detailed image.