Frustum Volume
Enter the two radii and the height.
Result
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Enter numbers to see the result.
Lateral surface area
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Slant height
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Formula: V = (1/3) pi h (R^2 + Rr + r^2). Lateral area = pi (R + r) s, with slant height s = sqrt((R-r)^2 + h^2).
Compute the volume of a frustum (a truncated cone) from the two radii and the height.
Enter the two radii and the height.
Enter numbers to see the result.
A frustum is what remains when the top is sliced off a cone. Its volume is (1/3) pi h (R^2 + Rr + r^2): notice that setting the top radius to zero recovers the familiar cone formula (1/3) pi R^2 h, a nice consistency check.
The slanted side unwraps into a ring sector. Its area is pi (R + r) s, where the slant height s = sqrt((R - r)^2 + h^2) comes from Pythagoras on the side profile. Buckets, lampshades, and planters are all frustums.