Cone Frustum Surface Area Calculator

About this calculator

A frustum is what remains of a cone after its tip is sliced off by a plane parallel to the base, leaving two circular faces of different radii (r1 and r2) connected by a slanted lateral surface. Its lateral surface area is π(r1 + r2) × s, where s is the slant height found from the Pythagorean relationship s = √(h² + (r1 − r2)²); adding the two circular end caps, πr1² and πr2², gives the total surface area.

This shape and its formulas are everywhere in manufacturing and design: paper and plastic cups, lampshades, buckets, funnels, traffic cones with flattened tops, and pipe reducers are all frustums, and knowing the surface area is essential for calculating how much material (sheet metal, cardboard, plastic) is needed to produce them at scale. Architects and engineers also use frustum geometry for tapered concrete columns, silos and chimney sections.

This calculator takes the two radii and height of a truncated cone and returns both its lateral and total surface area.