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Atmospheric pressure drops as you go higher up in the atmosphere. Pressure at sea level is around a thousand millibars. Five kilometers (about 16 thousand feet) up pressure is only about half as much.
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Original artwork by Windows to the Universe staff (Randy Russell).

How Pressure Changes with Altitude in Our Atmosphere

Air gets 'thinner' with increasing altitude. That's why mountain climbers sometimes need bottled oxygen to breathe, and why it is so easy to get 'winded' while hiking in high mountains or even visiting someplace at elevation. Atmospheric pressure is around 1,014 millibars (14.7 pounds/inch2) at sea level. At an elevation of 10 km (6 miles or about 30,000 feet), roughly the height of Mt. Everest, pressure drops to 265 millibars. That's less than 30% of the pressure at sea level! Both atmospheric pressure and the density of air decrease with altitude.

Last modified July 27, 2009 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF