How it works
Area = π × a × ba and b are the semi-axes (half-widths)
- a
- the semi-axis in one direction
- b
- the semi-axis at right angles to it
- π
- pi, about 3.14159
Use the semi-axes, the distances from the centre to the edge, not the full widths. If you have the full axes, halve each one first.
Frequently asked questions
What is the area of an ellipse with semi-axes 5 and 3?
About 47.12 square units, from π × 5 × 3.
What is the formula for the area of an ellipse?
Pi times the product of the two semi-axes, π a b.
What is a semi-axis?
Half of an axis, measured from the centre of the ellipse to its edge.
Is a circle a special ellipse?
Yes. When both semi-axes are equal, the ellipse is a circle and the area is π r².