Ellipse Calculator

Calculate the area, perimeter, eccentricity and focal points of an ellipse.

Ellipse calculator

Semi-major axis a

Semi-minor axis b

Area: —

Perimeter: —

Eccentricity e: —

Focal distance c: —

Semi-latus rectum: —

The foci lie on the major axis, at plus or minus c from the centre.

Common questions about the free online ellipse calculator.

Enter the semi-major and semi-minor axes. The area is pi times a times b, shown together with the eccentricity.

Eccentricity measures how stretched the ellipse is. It is the square root of one minus b squared divided by a squared.

The foci sit on the major axis at plus or minus c from the centre, where c is the square root of a squared minus b squared.

It uses Ramanujan's approximation, which is very accurate for ordinary ellipses and far better than a simple circle formula.

The tool always treats the larger value as the semi-major axis, so the eccentricity and the foci stay correct either way.

No. All ellipse calculations run locally in your browser, so your numbers never leave your device at any time.

Yes. The calculator is fully responsive and works on desktop, tablet and phone screens of any size.

Yes. The ellipse calculator is completely free, unlimited and requires no account, sign-up or installation.

Last updated: October 10, 2026