When to use this calculator
Find orbital eccentricity from extreme orbital distances. Distances are centre-based, not surface altitudes; applies to a bound ideal ellipse.
Explore the orbits & escape calculators for other questions in this topic. For a related calculation, use the Escape Velocity Calculator: Find ideal escape speed from a spherical body at a chosen centre distance.
PUTTING IT INTO PRACTICE
Elliptical Orbit Eccentricity: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Apoapsis distance from centre | 12 |
| Periapsis distance in same units | 8 |
| Result | 0.2 |
- Check the input labels and enter the example values above.
- Apply the relationship: Eccentricity = (apoapsis−periapsis)/(apoapsis+periapsis).
- The result is 0.2 , rounded for display.
How to interpret your result
Distances are centre-based, not surface altitudes; applies to a bound ideal ellipse.
Use radius from the centre of the attracting body, not altitude above its surface. Choose the gravitational parameter of the correct primary. Drag, rotation and other bodies are excluded from these simple models.
Frequently asked questions
Can I use altitude directly as orbital radius?
No. Add the central body’s radius to altitude when a formula requires distance from its centre.
When is the elliptical orbit eccentricity calculator useful?
Find orbital eccentricity from extreme orbital distances. Distances are centre-based, not surface altitudes; applies to a bound ideal ellipse.
How do I use the elliptical orbit eccentricity calculator?
Enter apoapsis distance from centre, periapsis distance in same units. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Eccentricity = (apoapsis−periapsis)/(apoapsis+periapsis).
What should I check before using the result?
Distances are centre-based, not surface altitudes; applies to a bound ideal ellipse.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see NASA: orbits and Kepler’s laws ↗. This is a topic reference, not an external review or endorsement of this tool.
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