Understanding common units of pressure is crucial in various fields, such as chemistry, physics, and engineering. Pressure is a fundamental concept that plays a vital role in processes involving gas, vacuum, and fluid systems. With numerous units available, such as Pascal (Pa), millimeters of mercury (mmHg), pound per square inch (psi), and torr, it’s essential to know their conversion relationships.

In this guide, we will explore the most commonly used pressure measurement units and their conversion relationships, making it easier for you to convert values across different applications.

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Common Units of Pressure

Common Units of Pressure

The SI Unit for Pressure: The Pascal

The Pascal (Pa) is the SI (International System of Units) unit for pressure, named after the French mathematician and physicist Blaise Pascal.

One Pascal is defined as the pressure of one newton per square meter (N/m²).

It represents the force applied uniformly over a unit area, making it an essential unit for quantifying pressure in various scientific and engineering applications.

Exploring Non-SI Units of Pressure

Pounds per square inch (PSI) is a non-SI unit of pressure commonly used in the United States and the United Kingdom.
It measures the force in pounds (lbs) applied to a square inch of surface area.
Originating from the customary system of units, PSI is widely recognized and employed in various industries as a convenient alternative to the Pascal.

The bar is a non-SI unit of pressure, where one bar is equal to 100,000 Pascals or approximately equal to the atmospheric pressure at sea level.
The term “bar” comes from the Greek word “baros,” which means weight.
A smaller unit derived from the bar is the millibar (mbar), with one bar being equivalent to 1,000 millibars.
Millibars are commonly used to represent smaller pressure variations.

An atmosphere (atm) is a non-SI unit of pressure, used to represent the average atmospheric pressure at sea level on Earth. One atmosphere is defined as 101,325 Pascals. The unit was established to provide a convenient and relatable reference point for pressure measurements in various scientific and engineering applications.

Inches of mercury (inHg) and millimeters of mercury (mmHg) are non-SI units of pressure, based on the height of a column of mercury in a barometer.

One inch of mercury is equivalent to the pressure exerted at the base of a column of mercury exactly one inch high at 0°C, whereas one millimeter of mercury corresponds to a mercury column exactly one millimeter high at the same temperature.
One inch of mercury equals 25.4 millimeters of mercury, or approximately 3,386.39 Pascals.

These units originated from the use of mercury barometers, invented by Italian scientist Evangelista Torricelli in the 17th century, to measure atmospheric pressure.

Inches of water column (inWC) and millimeters of water column (mmWC) are non-SI units of pressure that express the pressure exerted at the base of a column of water.

One inch of water column is equal to the pressure at the base of a water column exactly one inch high at 4°C, while one millimeter of water column corresponds to a water column exactly one millimeter high at the same temperature. One inch of water column is approximately equal to 249.089 Pascals.

These units have been used to measure pressure since the early days of fluid mechanics and are particularly useful in applications where low-pressure differentials are involved.

The torr is a non-SI unit of pressure, named in honor of the Italian physicist Evangelista Torricelli, who invented the mercury barometer. One torr is defined as 1/760 of an atmosphere, which is approximately equal to 133.32 Pascals.
A smaller unit derived from the torr is the millitorr (mTorr), with one torr being equivalent to 1,000 millitorr.
Torr and millitorr units are primarily used for measuring low-pressure environments, such as those found in vacuum systems.

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Conversion Relationships Between Pressure Units

Pascal to PSI Conversion

To convert pressure values from Pascals (Pa) to pounds per square inch (PSI), you can use the following formula:

1 Pa = 0.0001450377377 PSI

To convert from Pascals to PSI, simply multiply the pressure value in Pascals by the conversion factor:

Pressure (PSI) = Pressure (Pa) × 0.0001450377377

Bar to PSI Conversion

To convert pressure values from bars to PSI, you can use the following formula:

1 bar = 14.503773773 PSI

To convert from bars to PSI, simply multiply the pressure value in bars by the conversion factor:

Pressure (PSI) = Pressure (bars) × 14.503773773

Atmospheres to Pascal Conversion

To convert pressure values from atmospheres (atm) to Pascals (Pa), you can use the following formula:

1 atm = 101,325 Pa

To convert from atmospheres to Pascals, simply multiply the pressure value in atmospheres by the conversion factor:

Pressure (Pa) = Pressure (atm) × 101,325

Inches of Mercury to Millimeters of Mercury Conversion

To convert pressure values from inches of mercury (inHg) to millimeters of mercury (mmHg), you can use the following formula:

1 inHg = 25.4 mmHg

To convert from inches of mercury to millimeters of mercury, simply multiply the pressure value in inches of mercury by the conversion factor:

Pressure (mmHg) = Pressure (inHg) × 25.4

Inches of Water Column to PSI Conversion

To convert pressure values from inches of water column (inWC) to pounds per square inch (PSI), you can use the following formula:

1 inWC = 0.0361272918 PSI

To convert from inches of water column to PSI, simply multiply the pressure value in inches of water column by the conversion factor:

Pressure (PSI) = Pressure (inWC) × 0.0361272918

Extended reading: what is a pressure transducer?

pressure conversion chart

Pressure UnitAbbr.psiatminH2OcmH2Okg/cm²mmHgcmHgmbarPakPaMPa
Pounds per Square Inchpsi10.06827.6870.310.0703151.715.17168.9568956.8950.006895
Atmospheresatm14.71406.81033.291.0332760761013.25101325101.3250.101325
Inches of WaterinH2O0.03610.0025412.540.002541.8680.18682.491249.10.24910.0002491
Centimeters of WatercmH2O0.014220.0010.393710.0010.73530.073530.980798.070.098070.00009807
Kilograms per Square Centimeterkg/cm²14.2230.9678393.710001735.673.56980.798000980.098
Millimeters of Mercury (Torr)mmHg0.019340.0013160.53531.360.0013610.11.333133.30.13330.0001333
Centimeters of MercurycmHg0.19340.013165.35313.60.013610113.3313331.3330.001333
Millibarmbar0.01450.00098690.40151.01970.001020.75010.0750111000.10.0001

Read more about: Absolute Pressure Vs Gauge Pressure Measuring Instruments

Conversion Examples and Calculations

Here are three examples of converting pressure units using the pressure conversion chart provided earlier:

Example 1: Converting 0.5 PSI to Inches Water Column

From the table, we know that 1 PSI = 27.7076 inH₂O. To convert 0.5 PSI to inches of water column, we can use the following equation:

0.5 PSI * (27.7076 inH₂O / 1 PSI) = 13.8538 inH₂O

So, 0.5 PSI is approximately equal to 13.8538 inches of water column.

Example 2: Converting 100 kPa to Bar

From the table, we know that 1 kPa = 0.01 Bar. To convert 100 kPa to Bar, we can use the following equation:

100 kPa * (0.01 Bar / 1 kPa) = 1 Bar

So, 100 kPa is equal to 1 Bar.

Example 3: Converting 760 Torr to Atmospheres

From the table, we know that 1 atm = 760 Torr. To convert 760 Torr to atmospheres, we can use the following equation:

760 Torr * (1 atm / 760 Torr) = 1 atm

So, 760 Torr is equal to 1 atmosphere.

Frequently
Asked
Questions

Help Center

To convert PSI to kPa, use the conversion factor from the pressure conversion chart: 1 PSI = 6.89476 kPa. Multiply the PSI value by 6.89476 to get the equivalent value in kPa. To convert kPa to PSI, divide the kPa value by 6.89476.

Gauge pressure is the pressure relative to the atmospheric pressure, whereas absolute pressure is the pressure measured with respect to a perfect vacuum. Gauge pressure is the pressure value most commonly encountered in everyday situations, while absolute pressure is used in scientific and engineering calculations.

Yes, some pressure units are more common in specific industries. For example, inches of water column (inWC) and millimeters of water column (mmWC) are widely used in HVAC and plumbing. Similarly, inches and millimeters of mercury (inHg and mmHg) are commonly used in medical and meteorological fields.

More Pressure Measurement Solutions

In conclusion, understanding the Common Units of Pressure measurement and their conversion relationships is essential in many fields, including engineering, science, and industry. This knowledge helps to ensure accurate and consistent measurements across different systems and applications. The SI unit for pressure is the Pascal, but other common units include PSI, atmospheres, inches and millimeters of mercury, inches and millimeters of water column, and Torr.

By using the provided Common Units of Pressure conversion chart and conversion examples, you can easily convert between different pressure units. Remember that some units are more common in specific industries, so it’s crucial to choose the right unit for your application.

If you require high-quality pressure measuring instruments, we recommend Sino-Inst. As a professional supplier with extensive experience in the field, Sino-Inst offers a wide range of pressure measurement devices suitable for various industries and applications.Don’t hesitate to contact our knowledgeable team for any questions or assistance in selecting the right instrument for your application. Let Sino-Inst be your trusted partner in achieving accurate and reliable pressure measurements.

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