Diameter
noun
ちょっけい
周り (まわり) Circumference, Perimeter, Edge, Surroundings, Locality, Neighborhood
周囲 (しゅうい) Perimeter, Circumference, Surroundings, Environs
直径 (ちょっけい) Diameter
半径 (はんけい) Radius
The Diameter goes directly 直 through the middle of the cake けい
The chocolate cake ちょっけい Diameter is 42.