Orbital Period Calculator

Calculate orbital period and velocity using Kepler's Third Law
Kepler's Third Law: The square of the orbital period is proportional to the cube of the semi-major axis.
Mass of the central body
Average orbital radius
Orbital Period
Earth Days
Years
Hours
Orbital Velocity
km/s
m/s
km/h
Orbital Details
  • Circumference:
    km
  • Distance per Day:
    km
  • Revolutions/Year:
Kepler's Third Law Explained
Formula:
T² = (4π²/GM) × a³

Where:

  • T = Orbital period (seconds)
  • G = 6.674×10⁻¹¹ m³/(kg·s²) (Gravitational constant)
  • M = Mass of central body (kg)
  • a = Semi-major axis (m)
Simplified Form:
T = 2π√(a³/GM)

Key Insight: Objects farther from the central body take longer to orbit. For example, Mercury orbits the Sun in 88 days, while Neptune takes 165 years!

The orbital velocity also decreases with distance, following: v = √(GM/a)

Features

  • Calculate orbital period using Kepler's Third Law
  • Determine orbital velocity at any distance
  • Results in multiple time units (days, years, hours)
  • Preset configurations for all planets and major moons
  • Additional orbital statistics (circumference, distance traveled)
  • Detailed formula explanations

How to Use

  1. Enter the central body mass in kilograms
  2. Enter the semi-major axis (average orbital radius) in meters
  3. Or select a preset from the dropdown
  4. View the calculated orbital period, velocity, and other details