Frustum

A frustum is the part of a solid between two parallel planes.^[2] Most often, frustum refers to a truncated cone or pyramid. The word frustum is often misspelled frustrum.

A frustum based on a cone is called a conical frustum. A frustum based on a pyramid is called a pyramidal frustum.

Right Conical Frustum

Formulas for a right conical frustum:
R₁ is the radius of the smaller circle.
R₂ is the radius of the larger circle.
h is the height at the axis.
s is the slant height.
A is the surface area of the sides, not including the base and top.
V is the volume.

Right Pyramidal Frustum

Formulas for a right pyramidal frustum:
p₁ is the perimeter of the base.
p₂ is the perimeter of the top.
h is the height.
s is the slant height.
A₁ is the area of the base.
A₂ is the area of the top.
S is the surface area not including the base or top.
V is the volume.