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Name: Mark S.
Status: Student
Age: 30s
Location: N/A
Country: N/A
Date: May 2003

I am an art student and need help with a geometry issue. I am making teapots which are oval so the openings are ellipses. I need to create lids which are also then reshaped as ellipses to fit.

What I need to figure out is with a given ellipse is there a way to determine it's circumference to use as a guide for creating the same circumference of a circle lid?

The idea is that I use a wheel to throw the lids which makes them round then I compress them a bit to reshape them oval. It seems like as long as the two circumferences match they will fit?

According to "", there is no exact solution in closed form, but this approximation is very good:

PI * (3*(a+b) - sqrt((3*a+b)*(a+3*b)))

where 2*a is the length of the major axis (the largest measurement through the center) and 2*b is the length of the minor axis (the smallest measurement through the center).

Tim Mooney

The perimeter,P, of an ellipse that has a major axis, the long way, equal to: 2A, and a minor axis, the short way, equal to 2B is approximately: pi*(2(A^2 +B^2))^1/2 where pi = 3.14... And this is an approximation. The exact analytical answer is much more messy algebraically. I am not sure this is going to be of much practical value.

I have another suggestion of how you might approach the problem. A company, Alto Inc., sells supplies for matting photographs, art work, etc. They make elliptical templates that you could cut out of matting board, or cardboard, or some other "cut-able" material, and you could use the templates to serve as a guide for matching the pots and their lids. Cost is ~$60. Their e-mail is: and phone number: 1-800-225-2497. I do not do pottery, but this seems like a more practical and simpler solution. Since you could save the template(s), all the tea pots could be the same shape.

Vince Calder

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