Enter the semi-major (a) and semi-minor (b) axes and the calculator returns area, perimeter, eccentricity and focal distance.
Area = π × a × b, where a and b are the semi-major and semi-minor axes.
An ellipse perimeter has no simple exact formula; Ramanujan's approximation is extremely accurate and fast to compute.
A measure of how elongated the ellipse is: e = √(1 − b²/a²), where 0 is a circle and values near 1 are very stretched.