How do you measure the Earths curvature from city to city?

I'd assume there is such a function but i cannot find it. We can measure distance many ways and the curvature from point to point should be just as commonplace. Surely this is built in to Google Earth because we do have an accepted curvature formula. On a sphere Earth, lets say I want to know the curvature from LA to New York, how do I do that?

Thank you.