Texturing 3D sphere

Hey Everyone,
I am currently working on a project where i need to create and texture a 3D sphere in Papervision3D. The question that i have is what should the dimensions of the 2D image be in relation to the radius of the sphere. So say my sphere has a radius of 500 what would the width and height of the 2D image be? Does anyone know of a formula available to calculate these dimensions? Thanks.