How to Calculate Barometric Pressure
Convert between units of pressure.If you are not reading directly from a barometer, then you've probably been asked to convert a measurement from one unit of pressure to another., Know the units of pressure., Understand the origins of barometric...
Step-by-Step Guide
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Step 1: Convert between units of pressure.If you are not reading directly from a barometer
Learn the multipliers to convert between millibars, psi, atmospheres, and mm of mercury.Convert from inches of mercury to millibars: if you know the inches of mercury, simply multiply by
34.433. 1033/30=34.433{\displaystyle 1033/30=34.433} Convert from psi to mm of mercury: multiply the psi by
51.7. 760/14.7=51.7{\displaystyle 760/14.7=51.7} Convert from psi to inches of mercury: multiply the psi measurement by
2.041. 30/14.7=2.041{\displaystyle 30/14.7=2.041} Convert from inches of Hg (mercury) to mm Hg: multiply the measurement in inches by
25.33. 760/30=25.33{\displaystyle 760/30=25.33} -
Step 2: then you've probably been asked to convert a measurement from one unit of pressure to another.
Pressure is a measure of force per unit area, and there are various ways to describe both the force and the area.Atmospheric pressure is usually expressed in psi: pounds per square inch.
It can also be expressed in "atmospheres" – one atmosphere is
14.7 psi.
In the U.S., it is common to speak of air pressure in "inches of mercury," as one might read the pressure from a barometer.
In meteorology, air pressure is most often expressed in "millibars:" each millibar is exactly one dyne (gm-cm/sec^2) per square centimeter in the c.g.s. system of units.14.7 psi is a rough average of barometric pressure at sea level and at STP (standard temperature and pressure.) STP is an internationally-accepted "general state" of the atmosphere.
The
14.7 figure has been averaged over a large number of measurements, all either taken at sea level or corrected to sea level.
Atmospheres are rarely used in meteorology.The millibar is an especially convenient unit of pressure for atmospheric studies. 1033 millibars is the pressure equivalent to one atmosphere,
14.7 psi, or 30 inches of mercury.
Most weather maps and all aeronautical weather charts are in millibars, and the pressure at sea level is usually very close to 1000 millibars.
Nearly all barometers in the U.S. are graduated in units of inches of mercury.
The barometer is read to the nearest hundredth of an inch, such as "29.93 inches." Similarly, aircraft altimeter settings are universally given by control towers in inches of mercury corrected to sea level, regardless of the altitude of the airfield. , The Italian physicist Torricelli conceived the first barometer from the fact that the average pressure of the atmosphere is capable of "sucking" 76 centimeters (760 mm) of mercury (Hg, which is a liquid metal at STP) up the inside bore of an evacuated glass tube.
Later mathematicians have come up with other units of pressure, but the traditional unit remains mm Hg: millimeters of mercury. -
Step 3: Know the units of pressure.
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Step 4: Understand the origins of barometric measurement.
Detailed Guide
Learn the multipliers to convert between millibars, psi, atmospheres, and mm of mercury.Convert from inches of mercury to millibars: if you know the inches of mercury, simply multiply by
34.433. 1033/30=34.433{\displaystyle 1033/30=34.433} Convert from psi to mm of mercury: multiply the psi by
51.7. 760/14.7=51.7{\displaystyle 760/14.7=51.7} Convert from psi to inches of mercury: multiply the psi measurement by
2.041. 30/14.7=2.041{\displaystyle 30/14.7=2.041} Convert from inches of Hg (mercury) to mm Hg: multiply the measurement in inches by
25.33. 760/30=25.33{\displaystyle 760/30=25.33}
Pressure is a measure of force per unit area, and there are various ways to describe both the force and the area.Atmospheric pressure is usually expressed in psi: pounds per square inch.
It can also be expressed in "atmospheres" – one atmosphere is
14.7 psi.
In the U.S., it is common to speak of air pressure in "inches of mercury," as one might read the pressure from a barometer.
In meteorology, air pressure is most often expressed in "millibars:" each millibar is exactly one dyne (gm-cm/sec^2) per square centimeter in the c.g.s. system of units.14.7 psi is a rough average of barometric pressure at sea level and at STP (standard temperature and pressure.) STP is an internationally-accepted "general state" of the atmosphere.
The
14.7 figure has been averaged over a large number of measurements, all either taken at sea level or corrected to sea level.
Atmospheres are rarely used in meteorology.The millibar is an especially convenient unit of pressure for atmospheric studies. 1033 millibars is the pressure equivalent to one atmosphere,
14.7 psi, or 30 inches of mercury.
Most weather maps and all aeronautical weather charts are in millibars, and the pressure at sea level is usually very close to 1000 millibars.
Nearly all barometers in the U.S. are graduated in units of inches of mercury.
The barometer is read to the nearest hundredth of an inch, such as "29.93 inches." Similarly, aircraft altimeter settings are universally given by control towers in inches of mercury corrected to sea level, regardless of the altitude of the airfield. , The Italian physicist Torricelli conceived the first barometer from the fact that the average pressure of the atmosphere is capable of "sucking" 76 centimeters (760 mm) of mercury (Hg, which is a liquid metal at STP) up the inside bore of an evacuated glass tube.
Later mathematicians have come up with other units of pressure, but the traditional unit remains mm Hg: millimeters of mercury.
About the Author
Sandra Baker
Specializes in breaking down complex lifestyle topics into simple steps.
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