How to Calculate the Circumference of an Oval

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An oval looks like an elongated circle and is most commonly called an ellipse in geometry. Although there is no single, simple formula for calculating the circumference of an ellipse, one formula is more accurate than others. If you know the major axis and the minor axis of an ellipse, you can work out the circumference using the formula C = 2 x π x √((a2 + b2) ÷ 2), where a is the major axis and b is the minor axis. The major axis spans the length of the ellipse, running through the center and connecting the two farthest points, while the minor axis sits perpendicular to the major axis and connects the two closest points.

  1. Find Major and Minor Axes

  2. Note the major and minor axes of your ellipse and find the exponent of both. For example, if your major axis is 12 inches and your minor axis is 8 inches, work out (12 x 12) + (8 x 8) = 208.

  3. Divide Your Answer by 2

  4. Work out 208 ÷ 2 = 104. Insert this value into your formula. The next step is to work out C = 2 x π x √104.

  5. Find Pi Constant

  6. The value of π (pi constant) never changes. It is always 3.142. Work out 2 x 3.142 = 6.284. Insert this value into your formula. The next step is to work out C = 6.284 x √104.

  7. Find the Square Root

  8. Use a scientific or online calculator to find the square root of 104, which is 10.198. Insert this value into your formula. Work out 6.284 x 10.198 = 64.084. You now know that the circumference of the ellipse is 64.084 inches.


    • Check your answer by using an online circumference of ellipse calculator. Input the major axis and minor axis and compare the circumference of ellipse to your answer.


About the Author

Claire is a writer and editor with 18 years' experience. She writes about science and health for a range of digital publications, including Reader's Digest, HealthCentral, Vice and Zocdoc.