How Far Is Space From Earth? The Kármán Line Explained
Space is often said to begin about 62 miles (100 km) above sea level. See why the boundary is a convention, not a wall.
How Far Is Space From Earth? The Kármán Line Explained
Outer space is commonly said to begin at the Kármán line, 100 kilometers (about 62 miles) above sea level. Some U.S. contexts instead use an altitude of 50 miles, or about 80 kilometers. Neither value marks a physical cliff where all air suddenly ends; Earth's atmosphere gradually thins and extends far beyond either boundary.
What the Kármán line means
The 100-kilometer convention provides a practical reference for separating aeronautics from astronautics. It is useful for records, education and discussions of flight regimes, but different organizations may use different thresholds. The surrounding atmosphere still contains particles above that height; its pressure simply becomes extremely low. Therefore asking 'How far is space?' requires specifying whether you mean a conventional boundary, a particular orbit or the near-vacuum environment of interplanetary space.
Why 50 miles also appears in answers
The 50-mile standard has been used in certain U.S. astronaut recognition and aerospace contexts. It reflects a separate convention rather than a disagreement over the measurement of Earth's size. An aircraft does not suddenly cross into a completely airless environment at either altitude. Practical aerodynamic flight, the ability to sustain orbit and official astronaut labels are related but different questions. A good comparison gives both rounded values and explains who uses them.
Where the International Space Station orbits
The International Space Station typically operates hundreds of kilometers above Earth, far higher than the standard Kármán line. Even at that altitude, extremely thin atmospheric drag gradually affects spacecraft motion, which is why orbiting vehicles sometimes need reboosts. Being 'in space' does not mean being beyond Earth's gravitational pull. Astronauts aboard the station experience microgravity mainly because they and the station are continuously falling around Earth together in orbit.
Distance to the Moon is a different scale
The Moon is roughly 384,400 kilometers, or 239,000 miles, from Earth on average—thousands of times farther than the usual boundary of space. A rocket crossing 100 kilometers is nowhere near the Moon, and a brief suborbital flight is not an orbital mission. Distinguishing a boundary altitude from an orbital altitude and a destination distance prevents common misunderstandings about how far spacecraft must travel.
One altitude, several different flight regimes
A suborbital vehicle can cross 100 kilometers and then fall back without completing an orbit. An orbiting satellite generally must travel sideways fast enough to continue falling around the curved Earth rather than directly back to the surface. The 100-kilometer line is therefore not a magical threshold at which orbital flight begins. Similarly, pilots and astronauts may receive different official designations depending on the organization and era. Separating records and definitions from the physical requirements of orbit makes the answer much more useful than one altitude number alone.
Key takeaway
For an accurate answer, say which definition of 'space' you are using rather than presenting any conventional line as a hard atmospheric edge.
Frequently asked questions
How far up is the Kármán line?
100 kilometers, or about 62 miles, above mean sea level.
Why do some sources say space starts at 50 miles?
Some organizations use an alternate 80-kilometer convention for specific aerospace purposes.
Does Earth's atmosphere end at 100 km?
No. It becomes very thin but extends well beyond that altitude.