# Steradian facts for kids

The **steradian** (symbol: **sr**) or **square radian** is an SI unit. It is like a radian, but for smooth 3D objects, for example, a sphere. A steradian is about one twelfth the surface area of a sphere, regardless of how big the sphere is.

## Sphere vs Steradian

- The surface area of a sphere is
- The surface area of a steradian is just

So a sphere measures 4π steradians, or about 12.57 steradians. Likewise a steradian is 1/12.57, or about 8% of a sphere. And because we measure an angle, it doesn't matter what size the sphere is, it will always measure 4π steradians.

## See also

In Spanish: Estereorradián para niños

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Steradian Facts for Kids. *Kiddle Encyclopedia.*