Mercury barometers used to measure air pressure. Credit: Edal Anton Lefterov/Creative Commons

Pressure is a measurement of force per unit area. Unfortunately, there are many different units associated with pressure. The SI unit for pressure is the pascal (Pa). One pascal is equal to one newton per square meter (N/m^{2}). One pascal is a very small amount of pressure, so the kilopascal (kPa) is often used instead. Many atmospheric applications use the pressure unit millimeters of mercury (mmHg) as read from a mercury barometer. This example problem will show how to convert mmHg to kPa.

Example Problem: The pressure reading from a barometer is 767 mmHg. Express this reading in kilopascals, kPa.

Solution: The relationship between mmHg and Pascals is: 760 mmHg = 1.013 x 10^{5} Pa. There are 1000 Pa in 1 kPa.

Multiply 767 mmHg by the conversion factors above.

? kPa = 102.23 kPa

Answer: The barometer’s reading is equal to 102.23 kPa.