Measuring vacuum means assigning a number to the absence of matter in a space. In practice, what is measured is the amount of negative pressure in a given volume of space. There is no universal unit of measurement for vacuum, so Hydroscand uses the units relevant to each specific application. Here, you will find vacuum conversion, scales, and methodologies used in relevant industries.

Our vacuum converter makes it easy to quickly convert from kilopascal (kPa) to other common units such as millimeters of mercury (mmHg), Torr, PSI, and bar.

Vacuum is defined as a state in which the pressure is lower than atmospheric pressure. This results in a reduction of air or gas, creating a negative pressure relative to the surrounding environment.

 The term high vacuum describes conditions where the pressure is extremely low, that is between  10⁻³ mbar (0,001 mbar) and 10⁻⁷ mbar (0,0000001 mbar). In high vacuum there are very few gas molecules, which creates an environment with low air density and collisions between molecules are rare.    

To create high vacuum often a two-step process is used. First the pressure is reduced using pre-vacuum pumps such as rotating lamella pumps until 1 mbar level is obtained. Then high vacuum pumps like turbo molecular pumps lower the pressure until high vacuum level. 

High vacuum is essential in industries and research fields where purity and low pressure are critical:

• Semiconductor Manufacturing: The production of microchips and electronic components requires ultra-clean environments that can only be achieved in high vacuum.
• Surface Coating (PVD and CVD): Thin films of materials such as metals or ceramics are applied in a vacuum to create protective or functional layers.
  
• Research and Particle Accelerators: Vacuum environments minimize interference from gas molecules in physics and chemistry experiments.
• Space Technology: Vacuum chambers simulate space conditions for testing satellites and spacecraft.
  
• Electron Microscopy: High vacuum enables high-resolution imaging in advanced microscopes.

Vacuum is measured using different instruments depending on the level of vacuum and the desired precision.  Measuring pressure lower than surrounding (atmospheric) pressure requires methods adapted to low vacuum, middle- and high vacuum. 

Common units of measure for vacuum:

• Pascal (Pa): The SI-unit used for pressure where lower values indicates higher vacuum.          

• Millibar (mbar): Commonly used for industrial purposes.  

• Torr (mmHg):  Traditional unit mostly used for scientific purposes or applications. 

• Bar (bar): General unit for pressure level. 
  

Selection of vacuum measuring device og gauge is based on vacuum level, application and need for accuracy.   These are the main types used in our indutry:

• Low vacuum (Atmosfär till 1 mbar):  . Manometric gauges

• Middle vacuum (1 mbar till 10⁻³ mbar): Mechanical gauges 

• High- and ultra high vacuum  (10⁻³ till 10⁻¹⁰ mbar): Electronic gauges
  

Manometric vacuum gauges use fluids incapsuled in a column to measure differences in pressure.   One example is the U-tube manometer, where the difference of fluid level of two tubes indicate the pressure.  These gauges are very robust and does not use power to operate, but are unsuitable for high vacuum. As they typically use mercury as medium they require careful installation and care.  

Mechanical vacuum gauges measure vacuum by registering deformation in a flexible component, such as a diaphragm or Bourdon tube. When a pressure difference occurs, the component bends or deforms, and this movement is converted into a pressure reading. Mechanical gauges are primarily used in low and medium vacuum ranges, from about 1 mbar to atmospheric pressure. These gauges are easy to use and cost-effective, but they lack the precision required for high vacuum measurements.

Electronic vacuum gauges are advanced instruments used to measure high- and ultra high vacuum. These gauges convert the vacuum level to electric signals based on principles such as heat transfer, electric conductivity or ionization of gas molecules.  They offer high precision and a wide range, from mid- to ultra high vacuum (a few Pascal to 0⁻¹⁰ Torr).   However, they require regular calibration and relative high investment. 

• Pirani gauges: Utilize the thermal conductivity of gases. A heated wire loses heat to the surroundings, and this loss decreases at lower pressures because fewer gas molecules are available to transport the heat.

• Cold cathode gauges: Create plasma in the measurement chamber by ionizing gas molecules. The resulting ion current is proportional to the gas pressure.

• Hot cathode gauges: Use thermal electron emission from a heated wire. The emitted electrons collide with gas molecules and generate a measurable ion current that is linear with the pressure.

To make it easier to compare and convert between units used to measure vacuum, we present this basic conversion table. 

The table of comparisons below makes it easy to convert between different pressure units and vacuum levels. It is separated in columns using different units, such as atmospheric (ATM), water bar, mercury bar (mmHg), PSI and vacuum percentage. 

The International System of Units (SI -Système International d'Unités) standardizes units of measure for physical entities such as lenght, weight, time and pressure.  The SI system safeguards that scientific and technical measurements are consistent and comparable all over the world.  For pressure, Pascal (Pa) is the official SI unit. This is defined as 1 Newton pr square meter; (N/m²).