Pressure Calculator

Barometric pressure is the pressure within the Earth's atmosphere. It measures the force that the atmosphere exerts per 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.

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 the height of the mercury column due to pressure variation.

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 particular 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).

The most commonly used units of pressure are:

• Pa – pascals — it's the SI unit equal to one newton per square meter;
• psi – pounds per square inch — 1 psi approximately equals 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 1 mmHg and approximately equals 133 Pa; and
• atm – standard atmosphere — 1 atm equals 101,325 Pa.

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; and

• Gigapascals (1 GPa = 1,000,000,000 Pa) for material stiffness or tensile strength.

The value of standard pressure depends on the organization that establishes it but is usually 100 kPa or 101.325 kPa, which is approximately 14.5 psi or 14.7 psi. However, a few other standard pressure definitions are also 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.

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 the particles' energy and velocity, which generates greater force.

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.

To find the 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 particular 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 checking if they sum up to the total pressure.

High barometric pressure is a 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.

Osmotic pressure is the required pressure to prevent liquid flow across a semipermeable membrane that 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 in concentrations by the temperature and ideal gas constant R = 8.31 J/K⋅mol.

Partial pressure is the pressure that a particular gas mixture component would have at 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.

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.