Enter any two of the three variables in Kepler’s third law; mass, orbital radius, and time. The calculator will solve for the miss variable.

## Kepler’s Third Law Formula

The following formula is created through Kepler’s third law of orbital motion.

G · m · t² = 4 · π² · r³

- Where G is the gravitational constant
- m is mass
- t is time
- and r is orbital radius

This equation can be further simplified into the following equations to solve for individual variables.

M= 4 · π² · r³ /t²*G

T = square root (4 · π² · r³ /m*G)

r = cube root (G · m · t²/4*π²)

## FAQ

**What is Kepler’s Third Law?**

This law states that the mass, orbital radius, and time are all related through the equation above.

**What is orbital speed?**

Orbital speed is the rate at which an object, typically called a satellite, rotates around a larger body due to a velocity and the force of gravity.