Fun With Numbers: Tonight's Episode - The Barometer

So... what IS the air pressure at altitude? Pilots have a rule of thumb that talks about 1" for every thousand feet.* (But who thinks in English units?)

A quick google turns up this as the top link:

http://www.sablesys.com/baro-altitude.html

The rule of thumb is (initially) 'down 10% for each km of altitude'...
...or (overall), 'down an additional 50% for each 5 km of altitude"

So we have:

at 1 km, 90% 3280' (~Mt.Greylock (3491'))
1.5 km 85% 4920' (~Mt. Marcy (5344'))
2 km 80% 6560' (~Mt. Washington (6288'))
3 km 70%
4 km 60%
5 km 50%

then
6 km 45%
7 km 40%
8 km 35%
9 km 30% (Everest)
10 km 25%

15 km 12%
20 km 6%
25 km 3%
30 km <1.5%

That's a pretty tenuous atmosphere, when you think about it.


*Bonus geekery: The OTHER rule of thumb is that you lose 3 degrees F of temperature for every 1,000 feet of altitude.