How does one go about calculating the expected equatorial bulge of the earth? When I do the calculation I do not get the expected increase in diameter. I get a difference in diameters (D| equator-D|poles) 21.9 km when it should be 42.7km. My calculation equates the reduced acceleration at the equator (9.85-0.0339 m/s^2) to a gravitational acceleration at an increased radius (r|pole + h, where h is the increased radius) and I derive h. If I had gotten an h larger than expected I would have said the difference is due to the earth's stiffness, but I don't even get that. I have what I think is a possible answer but before I go there I thought I'd see if anybody really knows other than my guesses.