How Far Is The Sky From The Ground?

Roughly 49-50 miles from the ground until you hit outerspace. A plane flies roughly about 6-7 miles from the ground. Hopefully this helps.

I guess it depends on how you define what the sky is.  If you mean our atmosphere, that begins at ground level, and goes up to infinity.  There is no real boundary between the atmosphere and space...as you go up, it merely gets thinner and thinner.  Even the "hard" vacuum of space has SOME gas and particles.. Merely very ratified.

If by the sky you mean that visible blue dome overhead, that is the ozone which is found in the stratosphere,  ranging between 6.21 and 31.1 miles above the surface.