Orbital Period Calculator (Kepler's 3rd Law)
Calculate the orbital period of a satellite or planet using Kepler's 3rd law.
About this calculator
The Orbital Period Calculator (Kepler's 3rd Law) on NumberCals is a free, mobile-friendly tool for anyone needing to calculate the orbital period of a satellite or planet using kepler's 3rd law. Enter your values in the form below and the result is computed instantly — no sign-up, no installation, no waiting.
Formula used
T = 2π·√(a³/GM)
What you'll need
- Central Body
- Central mass (kg, only if 'Custom') (e.g. 5.972e24)
- Semi-major axis (m) (e.g. 6.778e6)
What you'll get
- Orbital Period (s)
- Orbital Period (min)
- Orbital Period (hours)
- Orbital Period (days)
- Orbital Period (years)
Formula
T = 2π·√(a³/GM)
Result
Frequently Asked Questions
What's Kepler's 3rd law? +
The square of a planet's orbital period is proportional to the cube of its semi-major axis: T² ∝ a³. Newton's gravitation gives the exact form: T² = (4π²/GM) · a³.
Example: ISS orbit? +
Semi-major axis ≈ 6.778 × 10⁶ m (Earth radius + 400 km altitude). Period ≈ 92.7 minutes — matches reality.
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