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Eccentricity of Ellipse Calculator

Online ellipse eccentricity: e=c/a measures flatness, range 0<e<1.

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e=c/a, 0<e<1
a>c
Focal distance

📖 Tutorial | Ellipse e

1. Definition
The ellipse eccentricity is e=c/a, c=√(a²−b²), range 0<e<1.
2. Formula & Notation
a,cAxis, focal distance
3. Properties & Laws
  • e=c/a;
  • 0<e<1;
  • Near 0 round, near 1 flat;
  • e=0 is a circle.
4. Steps
  1. Enter a>c>0;
  2. Click "Find e";
  3. Or click "Load Example".
5. Worked Examples
Example: 5,3: e=0.6.
6. Common Pitfalls
a>c;
e<1;
Find c from b first.

❓ FAQ | Ellipse e

Range?
0<e<1.
Meaning?
Flatness.
c?
√(a²−b²).
e=0?
Circle.
Example?
0.6.
Flatter?
Larger e.