Skip to main content

Kepler's Third Law Orbital Period Calculator

Johannes Kepler formulated his harmonic law in 1619, stating that the square of a planet's orbital period is directly proportional to the cube of its semi-major axis.

Distance from central body center to orbiting object in kilometers (e.g. Geostationary = 42,164 km).

Mass of primary body in kilograms (Earth ≈ 5.972×10²⁴ kg, Sun ≈ 1.989×10³⁰ kg).

Calculated Result
23.935 hours

Orbital Period (T)

Orbital Period (Days)

0.997 days (23.935 hours)

Orbital Velocity

3.075 km/s

Period in Years

0.00273 years

Period in Seconds

86,164.8 s

Calculation Breakdown

  1. Semi-Major Axisa = 42,164 km = 4.216e+7 m
  2. Kepler's Period LawT = 2π × √[a³ / (G × M)] = 23.935 hours (0.997 days)
  3. Orbital Speedv = √(G × M / a) = 3.075 km/s

Orbital Period vs Orbital Altitude (Earth Orbits)

Interactive visualization based on your current inputs

Period (hrs)
0.06.01218246,800 km (LEO)10,000 km20,000 km (MEO)26,560 km (GPS)42,164 km (GEO)Radius (km)Period (hours)

What Is the Kepler's Third Law Orbital Period Calculator?

Kepler's Third Law (Law of Harmonies) establishes the mathematical relationship between a celestial body's distance from its primary focus and its orbital revolution time.

How Does the Kepler's Third Law Orbital Period Calculator Work?

Gravitational attraction provides the required centripetal acceleration, linking gravitational force GMm/r² directly to angular velocity.

Kepler's Third Law Orbital Period Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

T = 2\pi \sqrt{\frac{a^3}{G \cdot M}}, \quad v = \sqrt{\frac{G \cdot M}{a}}

Orbital period T equals 2 pi times square root of semi-major axis cubed over gravitational constant times central mass.

How to Use the Kepler's Third Law Orbital Period Calculator

  1. Enter the orbital semi-major axis or orbital radius in kilometers.
  2. Specify the primary body mass in kilograms (Earth, Moon, Sun, or exoplanet host star).

Step-by-Step Example Calculation

Earth Geostationary Orbit (42,164 km)

Input Values:

semiMajorAxisKm:42164
centralBodyMassKg:5.972e24
Worked Steps: An orbital radius of 42,164 km produces an exact 24-hour sidereal orbital period with orbital speed 3.07 km/s.

Understanding Your Result

Period (Hours/Days/Years): Time required for one complete 360-degree orbital revolution.

Orbital Velocity (km/s): Average circular speed along the orbital trajectory.

Factors That Affect the Result

  • Orbital altitude directly increases orbital period; mass of the primary body compresses orbital period.

When Should You Use This Calculator?

  • Satellite mission trajectory planning, GPS constellation sizing, and exoplanet orbital modeling.

Assumptions & Limitations

  • Assumes two-body unperturbed Newtonian mechanics without atmospheric drag or third-body tidal perturbations.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Standard Newtonian two-body formulation using G = 6.67430×10⁻¹¹ m³/(kg·s²).

Explore more tools and calculators in Education Calculators