A worked example
A sphere with a radius of 3 has a surface area of about 113.1 square units.
Frequently asked questions
What's the difference between volume and surface area?
Volume measures how much space a shape encloses (cubic units); surface area measures the total area of its outer faces (square units) — useful for things like how much paint or wrapping material a shape would need.
Why does a cone's surface area need the slant height?
The cone's curved side isn't flat, so its area depends on the slant height (the distance from the tip to the edge of the base along the surface), not the vertical height — they're different measurements that happen to relate via the Pythagorean theorem.