What is the area formula for an ellipse?

Area equals pi times the two semi-axes multiplied together (A = π · a · b).

Why is the ellipse perimeter an approximation?

An ellipse perimeter has no simple exact formula, so this tool uses Ramanujan's second approximation, which is accurate to many decimal places for typical shapes.

What is eccentricity?

Eccentricity measures how stretched an ellipse is, from 0 (a circle) toward 1. It equals the focal distance divided by the semi-major axis.

Ellipse Calculator

Area, perimeter, eccentricity and axes of an ellipse.

Ellipse calculator

Enter the two semi-axes of an ellipse to get its area (π·a·b) and an accurate perimeter using Ramanujan’s approximation, plus the major and minor axes, focal distance and eccentricity. Everything updates instantly in your browser.