Surface Pressure Units
While Celsius and Fahrenheit are fairly familiar units of temperature, the units for measuring pressure are not so well known. Below are the possible units from the S'COOL report form, and a short explanation:- hPa - this is hectoPascals, or hundreds of Pascals (newtons per square meter, the metric unit of pressure), and is the preferred unit for atmospheric science and S'COOL. Standard atmospheric pressure is 1013.25 hPa, so your pressure will vary around this number.
- mb - this is millibar or thousandths of a bar, where a bar is approximately the same as an atmosphere. Millibars and hPa are equivalent so standard pressure is 1013.25 millibar.
- atm - this is short for atmosphere. Pressure at Earth's surface is nominally one atmosphere (1 atm); but of course varies slightly depending on the weather conditions.
- psi - this denotes pounds per square inch, and is the standard unit used in the aeronautical industry in the United States. Standard atmospheric pressure is 14.7 psi.
- inches Hg - this stands for inches of Mercury, and is the number given in most weather reports in the United States. Standard pressure is 29.92 inches Hg, so your reading should vary around this number.
- mm Hg - this stands for millimeters of Mercury. Standard pressure is 761.84 mm Hg.
- torr - this unit is named after the scientist Torricelli, and is another name for mm Hg; so standard pressure in this unit is also 761.84 torr.
| To convert from | to | multiply by: |
|---|---|---|
| atm | hPa | 1013.25 |
| inches Hg | hPa | 33.86 |
| mb | hPa | 1 |
| mm Hg | hPa | 1.33 |
| psi | hPa | 68.95 |
| torr | hPa | 1.33 |
For more help with unit conversions, here is a useful site: http://www.speckdesign.com/Tools2a.html.
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