Ellipse Calculator

Created by Bogna Szyk
Reviewed by Steven Wooding
Last updated: Aug 31, 2022

This equation of an ellipse calculator is a handy tool for determining the basic parameters and most important points on an ellipse. You can use it to find its center, vertices, foci, area, or perimeter. All you need to do is write the ellipse standard form equation and watch this calculator do the math for you.

We wrote this article to help you understand the basic features of an ellipse. Read on to learn how to find the area of an oval, what is the focus of an ellipse, or how do you define the eccentricity.

If you like the ellipse calculator, try the octagon calculator, too!

What is an ellipse?

An ellipse is a generalized case of a closed conical section. It is oval in shape and is obtained if you slice a cone with an inclined plane. In the case when the inclination angle of the plane is equal to zero, you get a circle (circles are a subset of ellipses).

ellipse
Source: Wikimedia

If you want to draw an ellipse, you must determine two points, called foci (points F₁ and F₂ in the image above). Then, the ellipse is defined as a set of all points for which the sum of distances to the first and the second focus is equal to a constant value. In a circle, both foci overlap at one point.

Ellipse standard form

The equation of an ellipse is a generalized case of the equation of a circle. It has the following form:

(x - c₁)² / a² + (y - c₂)² / b² = 1

where:

  • (x, y) – Coordinates of an arbitrary point on the ellipse;
  • (c₁, c₂) – Coordinates of the ellipse's center;
  • a – Distance between the center and the ellipse's vertex, lying on the horizontal axis; and
  • b – Distance between the center and the ellipse's vertex, lying on the vertical axis.

If the ellipse is horizontal (i.e., it is a circle "stretched" along the horizontal axis), then a is greater than b. If it is vertical, then b is greater than a. For the parameters a = b the ellipse is a regular circle of radius a and the following equation of a circle:

  • (x - c₁)² + (y - c₂)² = a²

What is the ellipsis area formula?

If a and b are the lengths of the semi-major and semi-minor axes, respectively, of your ellipse, then the area formula is:

A = π × a × b

In particular, if a = b, we obtain A = πa².

Looks familiar? You're right, we've recovered the formula for the area of a circle with radius a!

Surprisingly, finding the perimeter of an ellipse is much harder. There are many approximations that give solutions at various precision and accuracy levels. Our ellipse calculator uses the approximation given by Ramanujan:

Pπ(a+b)(1+3(ab)2(a+b)210+43(ab)2(a+b)2)\footnotesize P \approx \pi \, (a + b)\left(\!\frac{1 + 3\frac{(a-b)^2}{(a+b)^2}}{10 + \sqrt{4 - 3\frac{(a-b)^2}{(a+b)^2}}}\!\right)

Our ellipse standard form calculator can also provide you with the eccentricity of an ellipse. What is this value? Read on!

What is the eccentricity of an ellipse?

Eccentricity is the ratio of two values: the distance between any point on the ellipse and the focus; and the distance from this arbitrary point to the line called the directrix of the ellipse.

Every ellipse is characterized by a constant eccentricity. If the ellipse is a circle, then the eccentricity is 0. If it is infinitely close to a straight line, then the eccentricity approaches infinity.

Eccentricity is calculated with the use of the following equation:

  • eccentricity = √(a² - b²) / a for a horizontal ellipse; and
  • eccentricity = √(b² - a²) / b for a vertical ellipse.

Center, foci, and vertices of an ellipse

Apart from the basic parameters, our ellipse calculator can easily find the coordinates of the most important points on every ellipse. These points are the center (point C), foci (F₁ and F₂), and vertices (V₁, V₂, V₃, V₄).

  1. To find the center, take a look at the equation of the ellipse. The coordinates of the center are simply the numbers (c₁, c₂).
  2. The foci of a horizontal ellipse are:
    • F₁ = (-√(a²-b²) + c₁, c₂)
    • F₂ = (√(a²-b²) + c₁, c₂)
  3. The foci of a vertical ellipse are:
    • F₁ = (c₁, -√(b²-a²) + c₂)
    • F₂ = (c₁, √(b²-a²) + c₂)
  4. Vertices of an ellipse are located at the points:
    • V₁ = (-a + c₁, c₂)
    • V₂ = (a + c₁, c₂)
    • V₃ = (c₁, -b + c₂)
    • V₄ = (c₁, b + c₂)

There's another parameter related to conic sections called 'latus rectum', and you can learn about it in our latus rectum calculator!

FAQ

How do I calculate the area of an oval?

To find the area of an oval (ellipse):

  1. Determine the lengths of the radii (the semi-major and semi-minor axes, to use a more formal language).
  2. Compute the product of these radii lengths.
  3. Multiply the result of Step 2 by π, i.e., approximately, by 3.14.
  4. That's it! You've got the area of your oval!

What is the eccentricity of the ellipse with radii 4 and 5?

The answer is 3/5. To derive it, use the eccentricity formula e = √(a² - b²) / a, where a = 5 and b = 4. Plugging in the values, we obtain √(25 - 16) / 5 = 3/5.

Bogna Szyk
Ellipse with semiaxes, foci, center and vertices marked
(x - c₁)² / a² + (y - c₂)² / b² = 1
a
b
c₁
c₂
Eccentricity
Area
Perimeter
Center
x-coordinate
y-coordinate
First focus F1
x-coordinate
y-coordinate
Second focus F2
x-coordinate
y-coordinate
First vertex V1 (horizontal axis)
x-coordinate
y-coordinate
Second vertex V2 (horizontal axis)
x-coordinate
y-coordinate
First vertex V3 (vertical axis)
x-coordinate
y-coordinate
Second vertex V4 (vertical axis)
x-coordinate
y-coordinate
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