Frequently Asked Questions
Everything you need to know about the Surface Area Calculator.
What is surface area?
Surface area is the total area covering the outside of a 3D solid — the sum of the areas of all its faces or curved surfaces.
What's the formula for a cube's surface area?
SA = 6s², where s is the length of one side — six identical square faces.
What's the formula for a sphere's surface area?
SA = 4πr², where r is the sphere's radius.
How is a cylinder's surface area calculated?
SA = 2πr² + 2πrh — the two circular end caps (2πr²) plus the curved lateral surface (2πrh).
What's the formula for a cone's surface area?
SA = πr² + πr√(r² + h²) — the circular base plus the lateral (slanted) surface, where the second term uses the slant height derived from radius and height.
How does the square pyramid formula work?
SA = b² + 2bl, where b is the base side length and l is the slant height of a triangular face — the square base plus four congruent triangular faces.
What is 'slant height' and how is it different from vertical height?
Slant height runs along the surface of a triangular face from the base to the apex, while vertical height is the straight up-down distance from base to apex — they're equal only for a flat shape, not a 3D cone or pyramid.
Why does the triangular prism need five inputs?
A triangular prism's surface area needs all three triangle side lengths (for the rectangular side faces), the triangle's height (for the two triangular end areas), and the prism's length.
What units does this calculator use?
The calculator is unit-agnostic — enter all dimensions in the same unit, and the surface area result will be in that unit squared.
Is this calculator free to use?
Yes, completely free with no sign-up, and it runs entirely in your browser.