Parametric component + Dome + Sphere

[saidriad71]

I am trying to create a parametric component which includes a sphere (also dome).
To draw this sphere or dome, we need a circle as geometry and a special profile, so what is the exact equation between the radius of the circle and the sphere (also dome) for a perfect sphere, I mean for exemple a sphere with radius equal to 25 mm and not to 25.0012 mm. thank you for any help you could provide for me.