The stratosphere extends from roughly 10 kilometers (6.2 miles) to 50 kilometers (31 miles) above the Earth's surface.

It's important to note that this is not a hard boundary, and there is some variation depending on latitude and season. It's also not considered "space" as it's still within the Earth's atmosphere. The internationally recognized boundary of space is the Kármán line, located at 100 kilometers (62 miles) above sea level.