How High Is the ISS? Its Orbital Altitude Explained
The International Space Station normally flies between about 400 and 420 km above Earth’s surface — roughly 250 to 260 miles. That’s far above airliners, which cruise at around 10 km, yet it is still inside the very top of the atmosphere rather than deep space.
There is no single "one true" altitude: the ISS is kept in a corridor, and on a given day it sits somewhere in that band, typically within a few kilometres of 400 km. A live tracker always shows the current height, computed the instant you load the page.
Why this height, and not higher or lower
The altitude is a balance of three forces. Fly much lower and the wisps of atmosphere are thick enough to drag the station down quickly, costing fuel and risking re-entry; much higher and launching crew and cargo gets dramatically more expensive. Around 400-420 km, drag is manageable and launching is still affordable.
The choice is also anchored to history: the station’s Russian elements launch from Baikonur, at a latitude that restricts the minimum flight path angle, and the shared orbit was settled at roughly this corridor decades ago. The orbit page covers the inclination that goes with it.
Altitude is not fixed: drag lowers it constantly
At 400 km the station is still brushing against the exosphere. The very thin air produces a small but relentless drag, and every bit of slowing makes the orbit decay — which makes the next bit of drag worse, in a gentle feedback loop.
- Drag. Enough atmosphere exists at 400 km to measurably slow the station.
- Decay. Slowed, the station sags a little lower, where the air is slightly thicker. Left alone, the decay would eventually end in re-entry.
- Reboosts. Visiting vehicles and the station’s own thrusters periodically raise it back into the corridor — a "reboost" that each time nudges the orbit up by a few kilometres.
Between reboosts the altitude drifts back down, so the current height is forever changing within the band. If you ever see the altitude readout jump on a live tracker, that is usually a reboost, not a glitch.
Altitude, speed, and orbital period are all linked
The lower the orbit, the stronger the gravity pulling, the faster the station must move, and the shorter each lap takes. At ~400 km the ISS completes an orbit in about 93 minutes (about 15.5 orbits a day).
Extend that logic upward: a satellite at ~2,000 km (the top of "low Earth orbit") needs well over two hours per lap, GPS satellites at ~20,200 km take about 12 hours, and a geostationary satellite at roughly 35,800 km takes a full 24 hours to loop the planet exactly as fast as it spins. The ISS sits low and fast by design. More detail on the numbers is on the how fast is the ISS? page.
Altitude shapes what you can see from the ground
The height of the station decides how wide a circle of Earth sees it at any moment. From 400 km up, the geometric horizon is roughly 2,200 km away in every direction — a "footprint" about 4,400 km across. Anywhere inside that circle, a pass can rise above the local horizon.
A lower orbit shrinks that footprint and shortens how long the station stays in view; a higher orbit widens it but pushes the station farther away, dimming it. Because reboosts bounce the ISS between about 400 and 420 km, the exact horizon timing of a pass can shift a little from one prediction to the next — one more reason a tracker should always use the freshest orbital data, as explained in how ISS tracking works.
Curious what the station’s exact height is right now, or how low it has drifted this week? The live position page recalculates altitude and speed every second from the current elements.
See the ISS’s current altitude and speed live on the interactive map.
Track the ISS live