The cost of a fourth Yamato main turret

How much larger would the Yamato class need to be for four triple 18.1-inch turrets?

Potentially about twenty percent larger after the additional armour, ammunition, and machinery are counted.

Four triple 18.1-inch turrets could add as much as twenty percent to Yamato's displacement in this rough estimate. The extra barbette and turret are only the most visible additions. Armour and magazine volume must grow around the larger battery, while the ammunition supply becomes heavier. More machinery is then needed to drive the enlarged hull at the intended speed. The figure is a quick design estimate rather than a finished naval-architecture calculation.