Compute area, perimeter approximation, focal distance, and eccentricity of an ellipse.
Last updated: June 2026 | By Patchworkr Team
Enter both semi-axes as real numbers.
An ellipse has semi-major axis a and semi-minor axis b, with a >= b.
1. Enter the semi-major axis a and the semi-minor axis b.
2. Keep a greater than or equal to b so the focal-distance formula is valid.
3. Read the live area, perimeter approximation, and eccentricity.
For a = 5 and b = 3:
area = pi * 5 * 3 = 15pi
c = sqrt(25 - 9) = 4
Because a is the semi-major axis and the focal-distance formula uses sqrt(a^2 - b^2).
It uses Ramanujan’s approximation, which is accurate for most practical cases.
The ellipse becomes a circle, with c = 0 and eccentricity 0.
Yes, as long as they are finite positive numbers.
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