As simple it may sound, this is a fiddly topic to fiddle with. How high is space really? Officially, the first definition was coined by National Advisory Committee for Aeronautics (now NASA), which stated that space begins at the point where atmospheric pressure was less than one pound per square foot. That roughly measured up to 81 km.
That's lesser the distance from Kovai to Ooty (87.1 km), meaning you are closer to outer space than you think. Shortly thereafter, an aerospace engineer Theodore von Kármán calculated that in order for an aircraft flying up over 100 km to derive any lift, it would have to attain orbital velocity (30 km/s), now called the Kármán Line (100 km above sea level), a point where the aerodynamic lift ceases to exist.
Now, here are some facts. The International Space Station orbits at around 400 km above sea level. A typical airliner flies past at about 9km above sea level while military jets can fly as above as 30 Kms, which is close to the feat that Felix Baumgartner achieved by attempting a freefall in 2012, jumping from a height of 39 Km (Watch it here.). But where do the actual boundaries of space begin?
Unfortunately, nobody has tried to coin a standard definition of boundary for space. There's a reason for it. Simply because there is no way to measure where the boundaries of the space start. While there might be various definitions floating around, you simply can't fix an exact point where space starts. The further you move away from earth, the air gets thinner and thinner until there is no friction in the air, until you see the curvature of earth, until the sky that you've always known to be blue loses its color and ultimately turns black and you slowly move into a place so unknown that it will give you the scares.
I personally would define it as the height at which there is not enough oxygen left for a living being to survive. Well, there you go! Did you forget that space is a scary place?