# Why is it not possible to measure absolute vacuum or absolute pressures using barometers, which are based on atmospheric pressures?

**URL:** <https://forumautomation.com/t/why-is-it-not-possible-to-measure-absolute-vacuum-or-absolute-pressures-using-barometers-which-are-based-on-atmospheric-pressures/12328>\
**Category:** Pressure Measurement\
**Tags:** interviewquestions, pressure\
**Created:** [July 27, 2024, 7:06am UTC](https://forumautomation.com/t/why-is-it-not-possible-to-measure-absolute-vacuum-or-absolute-pressures-using-barometers-which-are-based-on-atmospheric-pressures/12328 "2024-07-27T07:06:58Z")\
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**Author:** ![Instrument\_Engineer](https://forumautomation.com/user_avatar/forumautomation.com/instrument_engineer/32/6734_2.png) [@Instrument\_Engineer](https://forumautomation.com/u/Instrument_Engineer)\
**Post date:** [July 27, 2024, 7:06am UTC](https://forumautomation.com/t/why-is-it-not-possible-to-measure-absolute-vacuum-or-absolute-pressures-using-barometers-which-are-based-on-atmospheric-pressures/12328/1 "2024-07-27T07:06:58Z")

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Why is it not possible to measure absolute vacuum or absolute pressures using barometers, which are based on atmospheric pressures?

 ![image](https://cdn.forumautomation.com/original/2X/2/2de1dfc9dff0e128ec03d5e2e51c0341e63f308f.png)

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**Author:** ![automation\_engineer6](https://forumautomation.com/user_avatar/forumautomation.com/automation_engineer6/32/7656_2.png) [@automation\_engineer6](https://forumautomation.com/u/automation_engineer6)\
**Post date:** [August 3, 2024, 8:47am UTC](https://forumautomation.com/t/why-is-it-not-possible-to-measure-absolute-vacuum-or-absolute-pressures-using-barometers-which-are-based-on-atmospheric-pressures/12328/2 "2024-08-03T08:47:05Z")

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Barometers, which are designed to measure atmospheric pressure, can’t measure absolute vacuum or absolute pressures due to their reliance on atmospheric conditions.

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Barometers are great for measuring atmospheric pressure, but they fall short when it comes to measuring absolute vacuum or absolute pressures. Here’s why:

1. **Dependent on Atmospheric Pressure** : Barometers work by measuring the pressure exerted by the atmosphere. They compare this pressure to a vacuum inside the barometer. Since they rely on the weight of the air above them, they can’t measure a true vacuum where there’s no air to exert pressure.
2. **Design Limitations** : Barometers are calibrated based on standard atmospheric pressure at sea level (101.3 kPa). They aren’t designed to handle the extremely low pressures of a vacuum or the variations in absolute pressure that extend far beyond the atmospheric range.
3. **Accuracy Issues** : For absolute pressure measurements, you need an instrument that can measure pressure in a completely air-free environment. Barometers can’t do this accurately because their readings are influenced by the presence and weight of atmospheric gases.

To measure absolute vacuum or absolute pressures accurately, you’d need a device like an absolute pressure gauge or a vacuum gauge. These instruments are specifically designed to measure pressure without relying on atmospheric conditions, giving you a true reading of the pressure in a given space.

I hope this helps clarify why barometers aren’t suitable for measuring absolute vacuum or absolute pressures! Feel free to ask if you have more questions .