About the Orbital Period Calculator
A satellite stays up because it falls around the planet as fast as it falls towards it. The time for one lap, the period, depends only on the mass of the planet and the distance from its centre. This calculator takes the body and the height of the orbit above its surface and gives the period, the orbital speed and the number of orbits per day. Type the body and the height above its surface and the orbital period appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Orbital Period Calculator
- 1Enter the body and the height above its surface.
- 2Pick the units or options from the menus if the orbital period tool offers them.
- 3Read the orbital period in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the orbital period
Space fans use it to understand satellites, students to practise Kepler's third law and writers to check science fiction. Engineers use the formula as the first step in planning a mission, choosing between low, medium and geostationary orbits.
The period increases with the 3/2 power of the radius: doubling the radius makes the period 2.83 times longer. A higher orbit is slower but takes longer, which is why a geostationary satellite moves at only 3.07 km/s.
How the orbital period is worked out
Period T = 2π × √(r³ ÷ (G × M)). Orbital speed = √(G × M ÷ r). Here r is the distance from the centre of the body (its radius plus the height). At 400 km above Earth, roughly the height of the International Space Station, the period is 92.4 minutes and the speed is 7.67 km/s, giving about 15.6 orbits a day. At 35,786 km the period is 23.9 hours, which matches Earth's rotation: a geostationary orbit.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Seven central bodies
- Height above the surface
- Orbits per day
Mistakes to avoid with orbital period
The formula assumes a circular orbit and a body that is much heavier than the satellite. The atmosphere at low height drags the satellite down, which is why the ISS needs regular boosts. The tool does not include the pull of other bodies, such as the Moon.
On phone and computer
On a phone, type into the boxes one after another and read the orbital period underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the orbital period move. The orbital period calculator works the same on both. Orbit time depends on distance and mass, and other space sums follow. Find the speed to leave a planet with the Escape Velocity Calculator, the pull between bodies with the Gravitational Force Calculator, and your weight elsewhere with the Weight on Other Planets Calculator.
Features
- Radius from the centre
- Higher means slower
- Atmosphere drags low orbits
- Clear messages when the orbital period inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate orbital period?
Period T = 2π × √(r³ ÷ (G × M)). Orbital speed = √(G × M ÷ r). Here r is the distance from the centre of the body (its radius plus the height). At 400 km above Earth, roughly the height of the International Space Station, the period is 92.4 minutes and the speed is 7.67 km/s, giving about 15.6 orbits a day. At 35,786 km the period is 23.9 hours, which matches Earth's rotation: a geostationary orbit.
What is the formula for orbital period?
Period T = 2π × √(r³ ÷ (G × M)). Orbital speed = √(G × M ÷ r). Here r is the distance from the centre of the body (its radius plus the height). The orbital period calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is a geostationary orbit?
A circular orbit over the equator with a period of one day, so the satellite hovers over the same spot.
Why do satellites in higher orbits move slower?
Gravity is weaker farther out, so the speed needed to stay in orbit is lower.
Can I use it for the Moon?
Yes. Choose the Moon and enter the height above its surface.
Is this orbital period calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.