If earth was a cube and you wanted measure the volume, wouldn't you need three variables instead of two? a x b x c = volume? Why only two variables (dimensions) to determine the volume of earth? Or were you using the word, dimensional in another sense?
If you were in the Navy you would have measured your position on earth with Latitude and Longitude, which is two dimensions. That’s all you would need. The sphere is taken as the surface only. Volume of a sphere adds a dimension, but then you aren’t dealing with the sphere itself.