Boiling Point of Water
Most charts giving the boiling point of water vs altitude, such as Table 1 below, are based on the standard atmosphere and can be a bit misleading. If the barometric pressure is different from the standard atmosphere, the actual boiling point of water will vary slightly from that given in the chart. In order to obtain an accurate value, one must also correct this value for the actual barometric pressure. The amount for this correction can be obtained from Table 2 below.
Or, to simplify this mind numbing process, you may enter your altitude and current barometric pressure into the form below, and, click "Calculate Boiling Point" to see an estimate of the boiling point of water under these conditions.
To determine your elevation in the United States, visit
National Map Viewer, or, the USGS
Seamless Data Distribution Viewer.
- From the left hand menu, select the Zoom
function by clicking on the magnifying glass with the plus sign.
Repeatedly click your mouse to zoom until you find your location.
- From the left hand menu, click on "Elevation" to select the Elevation function.
- On the map, click your location.
- Note your elevation (It will be displayed
in a pop-up window or below the map).
The barometric pressure value used to obtain the correction from Table 2 should be the current barometric pressure for your area as reported by your local weather station; or, you may visit The Weather Channel.
- Enter your city name or ZIP code on the home page to
look up your current weather conditions.
- Note your barometric pressure.
Note: These barometric pressure values are adjusted to sea-level so that 29.921 inches of mercury (inHg) is "normal" no matter where you live.
For example, using Table 1, we can see that, at sea level, and a barometric pressure of 29.921 inches of mercury (one atmosphere,) water boils at the "normal" 212°F. Then, using Table 2, and given a barometer at a slightly "low" 29.0, then water will boil 1.53°F lower, or 210.47°F; conversely, at a slightly "high" 30.8 inches of mercury, water boils 1.43°F higher, or, 213.43°F.
So, if you live in Denver, at about 5000 feet elevation, and, your local weather station reports 29.921 inches on their barometer, the real outside air pressure, obtained from Table 1, would be 24.896 inHg; and, so water would boil at 203.0°F. And, as above, if Denver were under a "low" pressure area, with the local weather station's barometer reading 29.0 inHg, then, using Table 2, you find that water will boil 1.53°F lower, or, at about 201.47°F.
To calculate the boiling point of water at a location on any specific day use the following equation:In the tables, the following equations have been used:
boiling point of water = boiling point at specified altitude (Table 1) ± boiling point barometric correction (Table 2).
pressure (in. Hg) = 29.921* (1-6.8753*0.000001 * altitude, ft.)^5.2559
boiling point = 49.161 * Ln (in. Hg) + 44.932
1. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 1997. ASHRAE Handbook - Fundamentals, Inch-Pound Edition. ASHRAE. Atlanta, GA.
| TABLE 1|| Changes in Standard Temperature and Pressure (in Hg) as a Function of Altitude|| (Ref. 1)|| TABLE 2|| Boiling Point as a Function of Barometric Pressure|| (Ref. 2)|
|Altitude (ft.)||Pressure(in. Hg)||Boiling pt.(° F)|| ||Pressure(in. Hg)||Boiling pt. (° F)||Boiling pt.[added or reduced](° F)|
2. Perry, R.H., Green, D.W., and Maloney, J.O. 1984. Chapter 6. Psychrometrics. Perry's Chemical Engineers' Handbook. McGraw Hill. New York, NY.