Frustum Lateral Area Calculator
Calculate lateral surface area of a frustum (truncated cone). Enter top radius, bottom radius, and height to compute the curved (lateral) surface area, plus both circular base areas.
Formula
Slant height: l = √(h² + (R−r)²); Lateral area = π(r+R)l; Total = Lateral + πr² + πR²
- Lateral (curved) surface area of frustum: π(r+R)l where l is slant height
- Top base area: πr²; Bottom base area: πR²
- Total surface area = lateral + both bases
Frustum with r=3, R=6, h=8
Inputs
- Top Radius (r): 3 cm
- Bottom Radius (R): 6 cm
- Height (h): 8 cm
Slant = √(64 + 9) = √73 ≈ 8.54 cm; Lateral = π(3+6)×8.54 ≈ 240 cm²; Top = π×9 ≈ 28.3 cm²; Bottom = π×36 ≈ 113 cm²; Total ≈ 381 cm²
Frequently asked questions
What is a frustum?
A frustum is a cone cut parallel to the base, removing the top. It has two circular bases of different radii.
What's the difference between lateral and total area?
Lateral area is just the curved surface. Total area includes both circular bases.