Cone Frustum Volume Calculator
Enter the bottom radius, top radius, and height of a truncated cone to get its volume instantly — in cubic units of whatever length unit you use.
Three measurements, one volume
Enter the bottom radius (R), the top radius (r), and the height (h) and the calculator returns the volume using V = (1/3)πh(R² + Rr + r²).
Use one unit
Keep all three inputs in the same length unit — the volume comes back in that unit cubed (cm gives cm³, inches give cubic inches).
What is a cone frustum?
A cone with the top sliced off
A conical frustum is what's left when you cut the pointed top off a cone with a slice parallel to its base, leaving two circular faces of different sizes joined by a sloping side. This frustum volume calculator turns three measurements — the wider bottom radius, the smaller top radius, and the straight-up height — into the volume the shape encloses. It's the number behind everyday objects shaped this way: buckets, plant pots, lampshades, drinking cups, and the tapered hoppers and silos used in industry. Because the formula is exact, it works at any size and in any consistent length unit.
Enter the bottom radius, top radius, and height to get the frustum volume instantly in cubic units.
The volume of a conical frustum is one-third of π times the height times the sum of the squared radii plus their product.
V = (1/3) × π × h × (R² + R·r + r²)Suppose a frustum has a bottom radius of 5, a top radius of 3, and a height of 10. First add the radius terms: 5² + 5×3 + 3² = 25 + 15 + 9 = 49. Then multiply by the height and π and take a third: (1/3) × π × 10 × 49 ≈ 513.13 cubic units. Setting the top radius to zero collapses this straight back to the cone formula (1/3)πR²h, and setting both radii equal turns it into a cylinder, πR²h — the frustum sits neatly between the two.
The formula is exact, but a couple of practical points are worth keeping in mind.
Right frustum, perpendicular height, consistent units
This calculator assumes a right conical frustum — the two circular faces are parallel and centred on the same axis. The height must be the perpendicular distance between those faces, not the slanted side length; if you only know the slant, work out the vertical height first. Keep all three inputs in the same length unit, or the volume will be wrong, and remember the result is a volume in cubic units, not a surface area or capacity in litres.