This section is from the book "The American Woman's Cook Book", by Ruth Berolzheimer. Also available from Amazon: The Domestic Arts Edition of the American Woman's Cook Book.
In the following list the measurements, in inches, are from extreme rim to rim.
Place Plate (also called cover plate, service plate, lay plate). 10 to 11 inches.
Dinner Plate (roast plate). 10 inches, but seen as large as 10 1/2 inches. The size of the dinner plate is fairly large, due to the current practice of placing attendant vegetables on the plate with the meat. The day of side dishes, each bearing a particular variety of vegetables, has definitely passed.
Entree Plate. 8 1/2 to 9 1/2 inches. A most convenient size, for, in addition to its use in serving entrees, it is often employed as a salad plate, or a fish plate: even a dessert plate when the finger bowl is borne in with the dessert silver on the plate, the finger bowl being removed later.
Dessert Plate. 7 1/2 to 8 inches. Used for miscellaneous desserts, and salads. It becomes the cake plate at tea.
Soup Plate. 8 to 8 1/2 inches at rim, for the usual type of soup plate with wide, flat rim. There is also a bowl soup plate, or "coup" soup, which has no rim at all. Soup plates are not as commonly used as at one time, due to the spreading favor accorded the cream soup cup and the bouillon cup for luncheons and informal meals.