Earth Orbit Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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A fast earth orbit estimate is valuable only when the setup is clear. Spaceflight and astronomy estimates are easiest to trust when you can separate measured inputs from model assumptions and derived values. The sections below show exactly what this page calculates, how to enter the data, and where the simplified model stops.

What this calculator does

The calculator isolates the relationship between Height, Orbital period and orbital period or orbit height. That makes it useful for testing how one input changes the answer without mixing in unrelated assumptions.

How to use it

Fill in Height, Orbital period exactly as defined on the page. Set Determine to match the solve path you want. After calculating, change one influential input slightly and confirm that the result moves in the direction predicted by the equation; this is a quick unit and setup check.

How the calculation works

For a circular Earth orbit, r = Rₑ + h and T = 2π√(r³/μ), using Earth’s gravitational parameter μ. The reverse path obtains r = [μ(T/2π)²]^(1/3) and then h = r − Rₑ. Circular orbital speed is √(μ/r).

Example

Choose Orbital period and keep the default 400 km height. The circular-orbit model gives an orbit radius of about 6.771×10^6 m and a period near 5,545 seconds, or about 92.4 minutes. If Height remains selected while the period field is blank, the current page instead asks for more input.

How to interpret the result

The orbital period or orbit height is a model-dependent astrophysical quantity. Keep track of whether distances are radii, altitudes, parsecs, light-years, or orbital semi-major axes, and do not interpret supporting approximations as direct observations.

Limitations and notes

The Determine selector and default-filled field are easy to misread: selecting Orbital period uses the entered height to calculate period, while selecting Height requires a period value. The default screen can therefore show Check inputs until the solve direction and populated field match. The model is circular Earth orbit only.