## Area

Unit
Surface area of the sphere with radius $$r$$. For example, if the radius is $$r = 1 \, \text{m}$$, then the surface area is:$$A ~=~ 4\pi \,\cdot\, (1 \, \text{m})^2 ~\approx~ 12.7 \, \text{m}^2$$

Alternatively, the surface area of the sphere can be expressed with the diameter $$d = 2r$$:$A ~=~ \pi \, d^2$

Pi is a mathematical constant and has the value $$\pi ~=~ 3.1415926...$$