Orbital Period Calculator (Earth Satellites)
How long a satellite takes to circle the Earth, from its altitude — the ISS laps the planet in about 93 minutes.
- Orbit radius (km)6,791
- Orbital period (minutes)92.8
- Orbital period (hours)1.55
- Orbits per day15.5
Inputs used
- Altitude above Earth420 km
About this calculator
Kepler's third law sets the rhythm of every orbit: the period depends only on the orbit's size and the mass being orbited — T = 2π√(r³/GM). For Earth, add the planet's 6,371 km radius to the satellite's altitude to get r, and the period follows.
The results explain the shape of the space around us. The ISS at ~420 km circles in about 93 minutes — 16 sunrises a day. GPS satellites at 20,200 km take close to 12 hours. And at 35,786 km the period hits exactly one day, so a satellite there hangs over the same spot forever — the geostationary belt where TV and weather satellites live.
The same law works for moons around planets: our Moon, 384,400 km out, takes 27.3 days, and Jupiter's Io, orbiting a far heavier planet, manages a full lap in 1.8 days. This calculator assumes a circular orbit around Earth.
Quick reference
Orbital period by altitude
Circular orbits around Earth: ISS, Starlink, GPS and geostationary altitudes.
| Altitude above Earth | Orbital period (minutes) |
|---|---|
| 400 km | 92.4 |
| 550 km | 95.5 |
| 1,000 km | 105.0 |
| 5,000 km | 201.1 |
| 20,200 km | 718.4 |
| 35,786 km | 1,435.7 |
Frequently asked questions
Why does the ISS orbit in 90 minutes but the Moon takes a month?
Orbital period grows steeply with distance — Kepler's third law says the period squared scales with the orbit radius cubed. The Moon is roughly 57 times farther from Earth's centre than the ISS, so its period is about √(57³) ≈ 430 times longer.
At what altitude is a geostationary orbit?
35,786 km above the equator. There the orbital period equals Earth's rotation (23 h 56 min), so the satellite stays fixed over one spot — which is why satellite dishes can be bolted down pointing one way.
How often do moons go around their planets?
Same law, bigger numbers: our Moon orbits Earth in 27.3 days; Jupiter's Io takes just 1.77 days, Europa 3.55 and Ganymede 7.15 despite the huge distances, because Jupiter's mass is 318 times Earth's; Saturn's Titan takes 15.9 days.
Results are informational only — not financial, medical or legal advice.