Volume for common 3D shapes — cube, box, sphere, cylinder or cone.
A cone with the same base radius and height as a cylinder always has exactly 1/3 its volume — that's why the cone formula is 1/3 × π r² h while the cylinder is the full π r² h. It's a geometric fact, not an approximation.
It's the surface area divided by the volume for the same shape and dimensions. A smaller ratio means less surface relative to volume — useful intuition for things like heat loss or material efficiency, where a more compact shape loses less per unit of volume.
It's the radius of the cone's circular base, and "Height" is the perpendicular height from the base to the apex — not the slant length along the cone's side. The calculator derives the slant height internally for the surface area figure.