The steradian (symbol: sr) or square radian[1][2] is the unit of solid angle in the International System of Units (SI). It is used in three dimensional geometry, and is analogous to the radian, which quantifies planar angles.

A steradian is used to measure solid angles. A steradian is related to the surface area of a sphere in the same way a radian is related to the...

In the International System of Units (SI), a solid angle is expressed in a dimensionless unit called a steradian (symbol: sr), which is equal to one square radian, sr = rad 2.

The steradian (symbol: sr) or square radian is the SI unit for solid angle. It is defined as the solid angle that, when projected onto a surrounding spherical surface, produces an area (of any shape) equal to the square of the radius of the sphere.

The steradian or square radian is the SI unit of solid angular measure. The symbol used to represent steradian is ‘sr’. It is used to measure two-dimensional angular span in three-dimensional space, similar to the radian which quantifies planar angles.

steradian, unit of solid-angle measure in the International System of Units (SI), defined as the solid angle of a sphere subtended by a portion of the surface whose area is equal to the square of the sphere’s radius.

The steradian, symbol sr, is the SI coherent derived unit for solid angle. One steradian is defined as the solid angle subtended at the centre of a unit sphere by a unit area of its surface. For a sphere of radius r, any portion of its surface with area A = r2 subtends one steradian at its centre.