At What Temperature Does Water Boil?

At what temperature does water boil?  The answer to this is easy, right?  It's 212 degrees Fahrenheit (100 degrees Celsius).  Right?  Isn't that what we were told in elementary and middle school?  It was, but there is a misconception regarding these numbers.  Water does boil at 212 degrees Fahrenheit....at sea level!  The boiling temperature of water decreases as elevation above sea level increases.

Why does elevation play a role?  The temperature at which water boils depends on the air pressure.  At higher elevations there is less air above the water and thus the air pressure is lower.  As a result, water molecules can more easily escape the pot of water and water boils at a lower temperature.  At most elevations this decrease in boiling temperature is minimal and nothing to really worry about.  At elevations that exceed several thousand feet, however, cooking instructions change to accommodate the lower boiling temperature.  Think about this for a second.  If you're trying to cook your macaroni in a pot of boiling water at a lower temperature, you need to cook it longer to maker sure the noodles are tender.

So how much does the boiling temperature change?  At 1000 feet the boiling temperature is 210.2 degrees F.  At 2000 feet the boiling temperature is 208.4 degrees F.  In Denver, CO (the mile high city), the boiling temperature is 202.5 degrees F.  That's about 10 degrees below the 212 degrees we think of as the boiling temperature of water.  If we go even higher, say 12,000 feet, the boiling temperature drops all the way down to 189.8 degrees F.  That's a big difference!

So the next time someone (maybe your kids) asks you about the boiling temperature of water, be sure to let them know that it is only 212 degrees F at sea level.  Everywhere else on Earth it is less than 212 degrees, and in some cases, 20+ degrees less.