# Thickness of Ocean Calculation

*Most recent answer: 09/19/2015*

- CHARLES MCCARTHY (age 75)

BOW, WASHINGTON, USA

Your method is correct- solve for the radii of the bigger and smaller spheres and take the difference. Your friend's method works here too but only because the extra volume is such a small fraction of the total. As a result, the outer and inner areas of the extra layer are almost exactly equal. So you can get the layer's volume by multiplying its thickness by the inner area.Your friend's approximation is so good here that it's the easier way to do the calculation, because you don't have to precisely calculate two big numbers (the radii) and then accurately take the difference. If the layer were thicker, those inner and outer areas wouldn't be equal and his method wouldn't work. Gravity has nothing directly to do with calculation.

Mike W.

*(published on 09/19/2015)*