How Iowa's inclined belt fits a distributed armour system

What vertical-belt equivalent should be used for Iowa or South Dakota, and why does the purpose of the model matter?

The value depends on the model; Iowa's inclined belt, backing, lower belt, and protective decks resist reduction to a universal equivalent.

A figure for a game depends on the rules used to model armour, while a historical model can describe the actual arrangement. Iowa's main belt is given as 12.1 inches of Class A armour on 30-pound-per-square-foot Special Treatment Steel, inclined 19 degrees inboard. A lower belt covers a much larger area beneath it. The deck protection includes an armour deck above the main belt, a bomb deck higher up, and a splinter deck below. Hull plating and torpedo protection add further parts to that arrangement. British and American procurement by weight per square foot explains why thickness alone is an incomplete description of an armour plate. A useful model must therefore state the material and geometry it is representing.