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How to Find the Diameter of an Ellipse

An ellipse is a geometric figure that results from the intersection of a cone by a plane. Ellipses are closed curves that are symmetric about their horizontal and vertical axes. Circles are a particular case of ellipse. The major and minor axes of an ellipse define its diameter. The major axis is the longest diameter of an ellipse; the minor axis is the shortest. A circle has only one diameter because its major axis is equal to its minor axis at all points.

Instructions

- 1
  Measure the distance between each focus point (a, b) and a single, shared point on the perimeter of the ellipse.
- 2
  Add the two distances together: (a + b). This is the diameter of the major axis.
- 3
  Square the result of the previous sum: (a + b)². Measure the distance between the two foci, (a, b).
- 4
  Square this distance, called f. Subtract the value from the squared value: ((a + b)² - f²).
- 5
  Take the square root of the resulting value of ((a + b)² - f²). The result is the diameter of the minor axis of the ellipse.

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