The atmosphere doesn’t have a single hard edge; it gradually thins out from Earth’s surface into space. If you mean the commonly used boundary, the Kármán line is about 100 km, or 62 miles, up.

Quick scoop

Earth’s atmosphere is usually described in layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The exosphere is the outermost layer and begins around 700 km above Earth, extending up to about 10,000 km in some descriptions.

The long answer

For everyday purposes, people often treat the atmosphere as ending around 100 km up. That’s the standard “edge of space” reference in many contexts, but it is not a sudden cutoff.

NASA notes that the exosphere is the highest layer and merges with the solar wind, while a 2019 study suggests Earth’s outer atmosphere may extend much farther via the geocorona, nearly 391,000 miles, or 629,300 km, into space. That means the answer depends on whether you mean the practical boundary, the named atmospheric layers, or the farthest trace of atmospheric particles.

Short version

  • Common boundary of space: about 100 km / 62 miles.
  • Exosphere begins: about 700 km up.
  • Farthest detected reach of Earth’s atmosphere: about 629,300 km in the geocorona.

If you want, I can also give you a simple layer-by-layer chart of the atmosphere.