Atmospheric Pressure

As we all know, atmospheric pressure is the force created by gravity acting on the air around us. So a basic unit of pressure is the 'atm'. One (1) atm or one atmosphere is not really a value as such. It is just a convenient way of expressing the amount of pressure we are subjected to in open air at sea level. As you go higher, say up a mountain, the air is thinner so the pressure is reduced. We can only live comfortably in a fairly narrow range of pressure. This range is not much outside of the one atm mentioned earlier.

Understanding Pressure

So for precise measurements of pressure, various methods were developed by scientists over the years and they came up with a whole lot of descriptions to suit different types of measurement. 

One of the simplest and easiest ways to understand pressure measurements is the use of the good old psi. Most of us know that we pump our car tyres up to around twenty six (26) psi or pounds per square inch. The psi is a fairly universal way of expressing pressure. The open air pressure we are subjected to is around fifteen (15) psi. The actual number is closer 14.696. That's where the one (1) atm comes from.

The obvious thing here is that to pump up a tyre to any pressure above atmospheric, that pressure has to be contained. The tyre wall squeezing against the wheel rim keeps the air in. So already we have discussed atm and psi. The same applies if we want to reduce the pressure below one (1) atm. The tyre or vessel or tank has to be sealed. So lets have a look at some other types of measurements.

Various types of pressure measurements

• kilopascals (kPa) Used in industrial applications
• millibar (mbar) Used for low pressure applications
• inches of mercury (inHg) Found in Barometers (similar to thermometers)

These are just a few of the various ways to describe pressure measurements so you see that it can get a bit confusing. But these different methods have been developed to suit different uses such as in industry, medicine and weather.

Many years ago a scientist named Blaise Pascal developed a system that became the international standard or the SI Unit for measuring pressure. Primarily today, kilopascals (kPa) are used in the air conditioning industry and for instruments to measure low values of pressure. 

Convert kPa to atm

Generally speaking one hundred (100) kilopascals (kPa) is equivalent to one (1) atm. But for accuracy there is a standard calculation for converting kilopascals to atm:

one (1) kilopascal (kPa) = 0.00986923 atm

An easy way to remember how to convert kPa to atm is that a thousand (1000) kPa is roughly equivalent to ten times atmospheric pressure. 

Danger of high pressure.

If you were standing near a tank that was pressurised to a thousand kPa and a weld or a seal burst open there would be quite a rush of air (or whatever was in the tank) suddenly trying return to normal atmospheric pressure. So watch out. Imagine hot oil or boiling water under pressure suddenly gushing out from a damaged tank. It is extremely important to design vessels correctly to be able to withstand pressures that they may be subjected to. 

So you can see the importance of knowing how to convert the various pressure methods from one to another. Instruments made in Europe are often set up to measure in kilopascals and in the US, particularly in oil and mining applications the instruments are set up to measure in bar.

If you are going to perform calculations of any type, including pressure measurements it is advisable to undertake further study of the science involved. Or you could discuss your issue with a professional technician or engineer qualified to work with instruments related to the measurement of pressure.

 

• MPa to psi
• psi to MPa
• MPa to ksi
• ksi to MPa
• kPa to psi
• psi to kPa
• kPa to atm
• atm to kPa