The boiling point calculator tells you what temperature water will begin to boil at the given altitude. The altitude can be input in both metric and imperial units, and even nautical miles should that situation come up. Elevation matters because of some simple laws of basic physics we'll be explaining later on down. Knowing what exact temperature water boils at your location assists with cooking, to help you time out tasks in meal preparation, and to adjust stove temperatures so, for example, your pasta turns out just the right grade of al dente.
When water boils, what's actually happening is that the temperature of the water has risen to the point where the liquid starts changing state into a gas. You can see this when you observe the boiling action: Those bubbles rising from the bottom are pockets of liquid turning into steam and rising to the surface. Water at sea level always boils at the same temperature: 100 degrees Celsius, or 212 degrees Fahrenheit. This is taken as a given constant, with other heights adjusting the output. Take an example such as Mount Elbert, Colorado, the highest peak of the Rocky Mountains and the highest elevation point in the United States. That elevation is 14,440 above sea level, and our calculator will tell you that a pot of water there will begin boiling at only 185 degrees Fahrenheit. What's going on here? What is actually affecting the water isn't the elevation at all, but the air pressure. "Air pressure" is a term you often hear on the weather forecast, but most people don't think about what that means. Basically, our atmosphere is another kind of "ocean," miles over our heads, with the same physics affecting it as those at the ocean depths. It has currents, waves, and greater pressure at lower depths just like the water in the ocean. Sea level and below is where the air pressure is heaviest, with air molecules getting denser there while they're thinner at higher elevations. The vapor pressure on the surface of the water has to equal the air pressure in order for the water to start the boiling action. Until then, the air pressure pushes down on the water, containing its energy until enough heat builds up to where active steam can escape. Amazingly enough, water can boil at room temperature! This is only possible if the air is removed altogether by means of a sealed environment and a vacuum pump, which is a common science experiment. There are several videos of this phenomenon on the Internet, available to the casual search. Notwithstanding, it's probably best to boil water in a pan on the stove; cooking is so much more convenient that way!