Ellipse Area
Enter the two semi-axes. Results update live.
Result
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Enter numbers to see the result.
Circumference (approx)
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Eccentricity
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Formula: Area = pi x a x b. Circumference uses Ramanujan's approximation; eccentricity = sqrt(1 - b^2/a^2).
Compute the area of an ellipse from the semi-major and semi-minor axes, with an approximate circumference too.
Enter the two semi-axes. Results update live.
Enter numbers to see the result.
An ellipse is a stretched circle, and its area stretches the same way: pi x a x b, where a and b are the semi-major and semi-minor axes. When a equals b you get a circle and the formula collapses to pi r^2, as it should.
Unlike area, ellipse circumference has no simple exact formula, so the tool uses Ramanujan's celebrated approximation, accurate to many decimal places for ordinary ellipses. Eccentricity, from 0 (circle) toward 1 (very flat), describes the shape.