Math CentralQuandaries & Queries


Question from michele:

i need to figure the circumference of an oval in mm if i am looking down on this my oval from side to side is 2.781 (inches) my top to bottom is 1.661 (inches) what is the overall circumference in mm? if you have a formula, please share it with me. i know how to convert inches to mm simply by dividing by 25.4

Hi Michele,

Sorry, there is no simple formula for the circumference of an ellipse (an oval).

There is however an approximation that you can find in our response to an earlier question. In the expression on this page a and b are the lengths of the semi-axes, so in your case a = 35.3187 mm and b = 21.0947 mm.


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