I was just trying to get the actual range of circumferences for the Earth depending on which way you measure (just based on math, of coure, I know the actual circumference could be considered nearly infinite depending on the length of your ruler). Wikipedia has a very nice table of stats: Ellipticity: 0.003 352 9 Mean radius: 6,372.797 km Equatorial radius: 6,378.137 km Polar radius: 6,356.752 km Aspect Ratio: 0.996 647 1 Equatorial circumference: 40,075.02 km Meridional circumference: 40,007.86 km Mean circumference: 40,041.47 km Now, here's the thing: I wanted to check their circumference numbers using their radius numbers. The mean radius does equal their mean circumference when you double it and multiply by pi. So does the equatorial radius agree with the circumference. But the polar (which I understand is synonymous with "meridional") radius yields 39940.65km, as opposed to the 40007.86 they actually list in the table. Does anyone have an answer for this? It looks like their numbers are what you will find anywhere, give or take a kilometer. Also, is the polar radius measured from geographic pole to pole or magnetic pole to pole?