# Pressure Calculator

By Dominik Czernia, PhD candidate
Last updated: Mar 18, 2021

With our pressure calculator, you can estimate the pressure which is exerted by force on a specific area of a surface. In the text below, we have explained what is pressure and what are the most common types of pressure. Read on if you want to learn about pressure definition and pressure formula. You can try our pressure conversion calculator to see how many different units pressure have and how you can calculate them.

## What is pressure?

As defined, pressure is a physical quantity which describes the magnitude of a force distributed on the surface of an object. We can distinguish many types of pressure due to the source of its origin. These are, for example:

• aerostatic pressure - the pressure inside the gas arising from its own weight. Check our air pressure at altitude calculator to find the atmospheric pressure at any altitude and temperature!
• hydrostatic pressure - analogous to the aerostatic pressure, but in this case, exerted by liquids.
• acoustic pressure - deviation from the average value of atmospheric pressure, occurring during the propagation of an acoustic wave in it. You can compute the pressure of sound with our dB calculator.

## Pressure definition

Our pressure calculator uses the straightforward pressure formula below:

`p = F / A`

where

• `p` is the pressure,
• `F` is the force,
• `A` is the area of the surface.

This pressure definition relates to the force which is applied perpendicularly to the surface of the object. You should remember that pressure is scalar and therefore it has no direction (as opposed to the force).

## Pressure measurement

Many techniques have already been developed for the measurement of pressure. Instruments which measure and display pressure are called pressure gauges. Usually, measurements are made relative to some specific pressure reference. We distinguish:

• absolute pressure which is zero-referenced against a perfect vacuum (our pressure calculator computes this pressure),
• gauge pressure which is zero-referenced against ambient air pressure (absolute pressure minus atmospheric pressure),
• differential pressure which is zero-referenced against other, specific value of pressure.

## FAQ

### What is barometric pressure?

Barometric pressure is the pressure within the Earth's atmosphere. It measures the force that the atmosphere exerts on the unit area. Another name for barometric pressure is atmospheric pressure. Barometric pressure heavily depends on weather conditions and altitude. At Earth's surface, it varies between 940 - 1040 hPa, or 13.6 - 15.1 psi.

### What measures air pressure?

You can measure air pressure using a barometer. There are many types of barometers, but the most common one is based on the changes in height of the mercury column due to pressure variation.

### How to calculate pressure?

1. Investigate what generates the pressure. Is it an object, liquid, or air?
2. Find the force that the source of pressure exerts on a certain surface.
3. Find the area of that surface.
4. Make sure that both values are in the correct units, i.e., newtons/meters squared or pounds/inches squared.
5. Divide the force by the area.
6. Your pressure will be expressed in pascals (Pa) or pounds per square inch (psi).

### What is the unit of pressure?

The most commonly used units of pressure are:

• Pa - pascals - it's the SI unit equal to one-kilogram per square meter.
• psi - pounds per square inch - 1 psi approximately equals to 6895 Pa.
• bar - it's the metric unit (not part of SI) equal to 100,000 Pa.
• mmHg - millimeter of mercury - 1 mmHg approximately equals 133 Pa.
• inHg - inch of mercury - 1 inHg approximately equals 0.49 psi.
• Torr - 1 Torr is almost the same as mmHg and approximately equals 133 Pa.
• atm - standard atmosphere - 1 atm equals 101,325 Pa.

### What is the SI unit of pressure?

The SI unit of pressure is the pascal, abbreviated to Pa. It is equal to one newton per 1 square meter (1 Pa = 1 N / 1 m2). The other commonly used SI units of pressure are:

• hectopascals (1 hPa = 100 Pa) to express atmospheric pressure.
• kilopascals (1 kPa = 1,000 Pa).
• megapascals (1 MPa = 1,000,000 Pa) in hydraulic systems.
• gigapascals (1 GPa = 1,000,000,000 Pa) for material stiffness or tensile strength.

### What is standard pressure?

The recently used values of standard pressure depend on the organization and are usually 100 kPa or 101.325 kPa, which is approximately 14.5 or 14.7 psi. However, there are also a few other standard pressure definitions currently in use. Standard pressure is the value of pressure defined by scientific and metrological organizations to allow comparisons between different experimental results in the same conditions.

### What causes air pressure?

Air pressure results from the movement and mutual collisions of the air particles, and the force that the particles exert on the surroundings. The higher the air pressure, the greater energy, and velocity the particles possess which generates greater force.

### What should my tire pressure be?

The recommended tire pressure usually ranges between 200 and 240 kPa or 30 and 35 psi. The exact value may depend on the vehicle and tire type, so you should look for your manufacturer's recommendation. This information should be on a label on the edge of your vehicle's door or on the tire itself.

### How do I find partial pressure?

1. Investigate what the components of the gas are.
2. Measure the total pressure of that gas.
3. Calculate the mole fraction for each component of the gas. It's the number of moles of a certain gas divided by the total number of moles for the entire gas.
4. Multiply the mole fraction of the first component by the total pressure.
5. Repeat the previous step for all components.
6. You can verify the results by adding all partial pressures together and check if they sum up to the total pressure.

### What is high barometric pressure?

High barometric pressure is pressure exceeding 1013.25 hPa, 14.7 psi, or 29.9 mmHg. This value corresponds approximately to the mean sea-level atmospheric pressure on Earth. Note, that "high barometric pressure" is a relative term. At high altitudes, where the pressure can be much lower, the aforementioned pressure values might be already very high for people living in such conditions.

### What is osmotic pressure?

Osmotic pressure is the required pressure for preventing the flow of liquid across a semipermeable membrane which splits two solutions with different concentrations. To calculate the osmotic pressure:

1. Find the difference between the concentrations of the split solutions.
2. Record the temperature in Kelvins.
3. Multiply the calculated difference by the temperature and ideal gas constant R.
4. Note, that Ideal gas constant R is approximately equal to 8.31 J per mol × K.

### What is partial pressure?

Partial pressure is the pressure that a certain gas mixture component would have in the same temperature and volume if it were on its own. The sum of partial pressures of all components is equal to the total pressure. You can calculate the partial pressure by multiplying the mole fraction of the gas component by the total pressure of the gas mixture.

### What is absolute pressure?

Absolute pressure is a pressure measured relative to the perfect vacuum, or, in other words, to the absolute zero reference point. The opposing term is gauge pressure which we measure against a certain pressure level. An example of absolute pressure is the forecasted barometric pressure from a weather report. The corresponding gauge pressure would be, for example, equal to the standard air pressure minus the actual atmospheric pressure.

Dominik Czernia, PhD candidate
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