Enter the distance from the center to the vertex and the distance from the center to the co-vertex to determine the ellipse foci. This calculator can also determine the distance from the center to the vertex or co-vertex given the other variables.

## Ellipse Foci Formula

The following formula is used to calculate the ellipse focus point or foci.

f = sqrt (a^2 – b^2)

- Where F is the foci
- a is the distance from the center to the vertex (also known as the center to the furthest point)
- b is the distance from the center to the co-vertex (center to shortest point

To calculate an ellipse foci, square the distance from the center to the vertex and square the distance from the center to the co-vertex, subtract the latter from the former, then take the square root of the result.

## Ellipse Foci Definition

An ellipse foci is defined as the locus of points in which the sum of the distance to each focus point is constant.

## Ellipse Foci Example

How to calculate an ellipse foci?

**First, determine the distance to the vertex.**Measure the furthest distance from the center to the edge of the ellipse.

**Next, determine the distance to the co-vertex.**Measure the closest distance from the center to an edge.

**Finally, calculate the foci.**Using the formula above, calculate the foci.

## FAQ

**What is an ellipse foci?**

An ellipse foci is the distance from the center of an ellipse to it’s focus points and is a measure of the elongation of the ellipse.