The definition of where space starts, at what altitude above the surface of the Earth, is not a clear cut thing.
This equation lets you see altitudes for various critical boundaries above the Earth's surface -- above sea level.
To provide a comparative reference, you can also select the summit of Pikes Peak or Mount Everest. These mountain summits are clearly nowhere near the boundary of outer space but they are two of the higher points on the planet's surface. The atmospheric density at Pikes Peak Summit is by comparison about 60% of that at sea level.
I have provided the following altitudes:
Note: all of these altitudes that are above the altitude of Mt Everest are loose approximations. It is not possible to define specific altitudes for these key boundaries. Even Pikes Peak's altitude has been redefined recently. You still see people running around Colorado with t-shirts that have the old altitude of 14,110 feet. It is officially these days defined as 14,115 feet. So even the altitude of mountain summits are not always concrete numbers.
This notion of boundaries is important because there is no definitive point at which you leave Earth's atmosphere and are suddenly in the total vacuum outer space. The further and further you go from the Earth's surface the thinner and thinner becomes the atmosphere. At the altitude of a geostationary orbit, there are small numbers of atmospheric molecules per volume. Go far enough from the Earth and you might find only one or the atmospheric molecules per cubic meter. Go even further and you might find there is less than one molecule of atmosphere on average per cubic mile. And there continues to be less remnants of atmosphere the further you go from the Earth.