# Absolute Pressure Examples

We explain the absolute pressure example. The absolute pressure is that at which **a substance or a geographical point is found** , **in relation to absolute zero** . It is the true pressure because it takes into account the atmospheric pressure and also the pressure that is being exerted. Its value is the one that is applied in the laboratory experimental calculations to have an accurate result.

To calculate the absolute pressure, the atmospheric pressure and the pressure in the system, either hydrostatic or gauge, are added:

**Absolute pressure = Gauge pressure + Atmospheric pressure**

**Absolute pressure = Hydrostatic pressure + Atmospheric pressure**

## What are the units of absolute pressure?

The units of measurement for absolute pressure are the same as those used for all types of pressure:

- Atmospheres (atm)
- Bars (bar)
- Pascals (Pa)
- Millimeters of mercury (mmHg)
- Pounds over square inch (psi)
- Kilogram force over square centimeter (kgf / cm
^{2})

### Absolute pressure in gases

The gases exert pressure against the walls of the container that contains them. This pressure is called gauge pressure, and it exists inside tanks, balloons, or tires, for example. It can be measured by means of devices called manometers. To obtain the absolute pressure of a gas, atmospheric pressure is added to the gauge pressure.

**Absolute pressure = Gauge pressure + Atmospheric pressure**

Atmospheric pressure is that of the environment and can be measured with devices such as the **barometer** or the **aneroid barograph** . Its value will be the one that marks the reading, and it will be different every day according to the weather conditions.

The gauge pressure can be higher or lower than atmospheric. When it is lower, it is said to be a **vacuum pressure** . It is the one found in deflated balloons or vacuum food packaging. In that case, the absolute pressure would be slightly higher than atmospheric.

## Absolute pressure in liquids

Liquids exert pressure when they are at rest, contained in a container. It is due to their weight and the height they comprise within the walls. It is the so-called hydrostatic pressure, and to obtain the absolute pressure, atmospheric pressure is added, because the latter also acts on the surface of the liquid.

**Absolute pressure = Hydrostatic pressure + Atmospheric pressure**

Substituting the formula for hydrostatic pressure **P _{H} = **

**ρ * g * h**is:

**Pabs = ****ρ * g * h + Patm**

**Pabs = ****P _{H} + Patm**

When there are two or more liquids inside the container, the hydrostatic pressure will be the accumulated pressure of all of them. In the end, the pressures that will act **on the bottom of the container** will be hydrostatic and atmospheric. That is the absolute pressure.

## Absolute pressure in solids

Solids exert pressure due to their weight and the area covered by their geometry. This will be accompanied by atmospheric pressure, which influences its surface and accumulates above the ground. To calculate the absolute pressure, the sum is made:

**Absolute pressure = Pressure + Atmosphere pressure**

Substituting the pressure formula **P = F / A** , it remains:

**Pabs = (F / A) + Patm**

## Examples of absolute pressure

### Example 1

Calculate the absolute pressure when the pressure is 240 Pascals. The atmospheric pressure that is taken into account is the standard one: 101325 Pascals.

**Pabs = P + Patm**

Pabs = (240 Pa) + 101325 Pa

**Pabs = 101565 Pa**

### Example 2

Calculate the absolute pressure when the pressure is 289 Pascals. The atmospheric pressure that is taken into account is the standard one: 101325 Pascals.

**Pabs = P + Patm**

Pabs = (289 Pa) + 101325 Pa

**Pabs = 101614 Pa**

### Example 3

Calculate the absolute pressure when the pressure is 264 Pascals. The atmospheric pressure that is taken into account is the standard one: 101325 Pascals.

**Pabs = P + Patm**

Pabs = (264 Pa) + 101325 Pa

**Pabs = 101589 Pa**

### Example 4

Calculate the absolute pressure when the pressure is 153 Pascals. The atmospheric pressure that is taken into account is the standard one: 101325 Pascals.

**Pabs = P + Patm**

Pabs = (153 Pa) + 101325 Pa

**Pabs = 101478 Pa**

### Example 5

Calculate the absolute pressure when the hydrostatic pressure is 5028 Pascals. The atmospheric pressure that is taken into account is the standard one: 101325 Pascals.

**Pabs = ****P _{H} + Patm**

Pabs = (5028 Pa) + (101325 Pa)

**Pabs = 106353 Pa**

### Example 6

Calculate the absolute pressure when the hydrostatic pressure is 2,015 bar. The atmospheric pressure that is taken into account is the standard one: 1,013 bar.

**Pabs = ****P _{H} + Patm**

Pabs = (2,015 bar) + (1,013 bar)

**Pabs = 3.028 bar**

### Example 7

Calculate the absolute pressure when the hydrostatic pressure is 4.5 bar. The atmospheric pressure that is taken into account is the standard one: 1,013 bar.

**Pabs = ****P _{H} + Patm**

Pabs = (4.5 bar) + (1.013 bar)

**Pabs = 5.513 bar**

### Example 8

Calculate the absolute pressure when the hydrostatic pressure is 6 bar. The atmospheric pressure that is taken into account is the standard one: 1,013 bar.

**Pabs = ****P _{H} + Patm**

Pabs = (6 bar) + (1.013 bar)

**Pabs = 7.013 bar**

### Example 9

Calculate the absolute pressure when the gauge pressure is 400 millimeters of mercury. The atmospheric pressure that is taken into account is the standard: 760mmHg.

**Pabs = ****Pman + Patm**

Pabs = (400mmHg) + (760mmHg)

**Pabs = 1160mmHg**

### Example 10

Calculate the absolute pressure when the gauge pressure is 320 millimeters of mercury. The atmospheric pressure that is taken into account is the standard: 760mmHg.

**Pabs = ****Pman + Patm**

Pabs = (3200mmHg) + (760mmHg)

**Pabs = 1080mmHg**