Vacuum Unit Conversion Chart – New ISM Resource

The new ISM Vacuum Pressures Unit Conversions Chart (Absolute and Relative) is now available as a downloadable PDF

A liquid column gauge or manometer. A sealed tube with 760 mm of Mercury held above a pan of mercury. The pressure of the mercury's weight within the tube equals the surrounding atmospheric air pressure. There is a space at the top closed end of the tube containing a vacuum.Introduction
Vacuum systems are used in a wide range of industrial, material handling, food processing and laboratory applications. Wherever vacuum is used, questions come up about vacuum or negative pressure. What it is, how it is measured and how one vacuum measurement unit compares to another.

The new Vacuum Pressures Unit Conversions Chart from ISM was created to help make component selection for vacuum applications faster and easier.

What is a vacuum and how is it measured?
Vacuum is an air pressure measurement that is less than Earth’s atmospheric pressure, about 14.7 psi. A perfect vacuum, by definition, is a space where all matter has been removed. This is an idealized description.

Vacuum pressures that come close to the “almost no matter” point are difficult and expensive to create. Industrial and laboratory applications require varying degrees of vacuum that are less than perfect vacuum. This is why it is useful to understand something about units used to measure vacuum and how to convert between them.


Get a copy of the new ISM Vacuum Unit Conversions Chart

Get a copy of the ISM Vacuum Pressures Unit Conversions Chart (Absolute and Relative)

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Modular Check Valves

We've taken spring-loaded check valves to a whole new level. Mix and match imperial and metric connections. Watch the video.

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Vacuum pressure units listed in the ISM Vacuum Unit Conversion Chart

  • ATM (standard atmospheres, 760 mm Hg)
  • PSIA (pounds per square inch, absolute)
  • PSIG (pounds per square inch, gauge)
  • Torr (millimeters of Mercury)
  • in Hg (inches of mercury)
  • kPa (kilopascals, newton-force per square meter)
  • bar (bars, kPa x 100)
  • mbar (millibars, bar x 1000)

Note: Pressure measurements given in inches or millimeters of water, mercury or some other liquid are based on the earliest instrument developed for measuring pressure, the liquid column gauge or manometer.

Vacuum or vacuum pressure measurements are described as either absolute or relative. Absolute pressure is measured from a zero point where zero represents a 100% or perfect vacuum. Relative pressure measurements are given in reference to ambient pressure, the atmospheric pressure in the surrounding area.

Factors that affect the consistency and usefulness of relative vacuum measurements

  • Ambient or atmospheric pressure varies with weather
  • Ambient or atmospheric pressure varies with altitude

Tips to keep in mind when evaluating and converting between vacuum units

  • PSI is based on the United States customary system (USCS or USC)
  • Familiar USCS units are the mile, foot, inch, gallon, second and pound
  • US customary measurements are unique to the US but are now defined in terms of metric standards
  • USCS units are widely used in commercial products made in or sold to the US market
  • The International System of Units (SI), is the modern metric system
  • SI is the most widely used measurement system worldwide

Learn more about the SI International System of Units.

Degrees of vacuum and vacuum levels for industrial and laboratory applications

A chart listing and describing conventional degrees of vacuum. Perfect Vacuum is 0 Torr (theoretically impossible). Outer Space is about 1E-9 to 1E-17 Torr. Extreme High Vacuum is about 1E-13 Torr. Ultra High Vacuum (UHV) is about 1E-10 to 1E-11 Torr. High or Hard Vacuum (HV) is about 1E-5 to 1E-8 Torr. Medium or Intermediate Vacuum is about 1E-3 to 1E-5 Torr. Low, Soft or Rough Vacuum is about 1E-3 Torr. Atmospheric Pressure is about 760 Torr.
Note: 1 atmosphere or 760 Torr is equal to about 14.7psi

Learn more about vacuum and vacuum measurement in the industrial environment.
(Fundamentals of Vacuum at Hydraulics and Pneumatics)

Get a copy of the ISM Vacuum Pressures Unit Conversions Chart (Absolute and Relative)

What kinds of problems have you had moving between different vacuum measurements when setting up or sourcing components for your application? Help us by telling others what you learned.

Have questions about vacuum or components for vacuum applications? If so, send me an email - You can also ask questions using the comments section below.

Additional resources


Steven C. Williams headshot March, 2018.

About the author
Steven C. Williams my LinkedIn profile link button.
Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing (ISM), an ISO 9001-2015 supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world. He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM.       

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