Pressure is defined as a force exerted on a surface per unit area. To put it more simply, it’s the force that is put on a certain defined area.
You’re probably most familiar with the concept as we use it in everyday life. For example, a doctor might say, “apply pressure to the wound,” in which case you would press on the wound (aka apply pressure).
But you’ve also heard this in a scientific and/or industrial context with air pressure, tire pressure, water pressure, etc. Often, you’ll see the units of pressure change depending on the context. Kilopascals (kPa) and pound-force per square inch (psi) are the two most common.
Sometimes, you’ll need to switch between those units. In this article, we’re going to take you through exactly how to go from kPa to psi, when you need to do that, along with more information on each of the units.
History of the Pascal
Like many scientific terms, the term “kilopascal” is named after a scientist. In the case of the Pascal, it’s named after a French mathematician, philosopher, and physicist named Blaise Pascal.
He worked extensively on hydraulics, fluid dynamics, physics, and hydrostatics. He also invented the calculator, syringes, and the hydraulic press.
To honor his work and legacy, the metric unit for pressure, the Pascal, was named after him.
A single Pascal is defined as 1 Newton per square meter (1 N / m^2). A Newton is a unit of force (equal to 1 kg * m * s^-2 if you were wondering).
Thinking back to the definition of pressure we gave you earlier, this makes sense. Pressure is the amount of force (Newtons) put on a certain area (square meter).
Onto Kilopascals. Look at the prefix “kilo”. Kilo means 1000. So 1 Kilopascal is equal to 1000 Pascals.
Use of kPa
kPa is used around the world (including the United States) for scientific study. It’s often used in engineering, physics, geophysics, chemistry, etc.
It’s also used almost everywhere for other applications of pressure like water pressure, air pressure, pressure tanks, tire pressure, etc. However, the United States doesn’t follow the metric system that the kPa unit is a part of, which is where the unit psi comes in.
As we said, psi means pound-force per square inch. You’ll often hear people refer to it as “pounds per square inch”, but the more accurate name is “pound-force per square inch”.
It’s equal to the pressure applied when one pound-force is applied to a one square inch area.
Where Did psi Come From?
The United States, unlike almost the entire rest of the world, doesn’t follow the metric system. That means instead of using meters, kilograms, and Newtons, the United States uses inches, pounds, and pound-force units.
That gives us pound-force per square inch (psi) units for pressure. It still gives you a unit of force per area, like the definition of pressure requires, but just in non-metric units.
This is called the “Imperial System” of measurement as opposed to the “metric system” of measurement used by the rest of the world. The Imperial System of measurement was actually developed by Britain (who ironically doesn’t use that system today) and was adopted by the United States in the late 1700s.
During the Industrial Revolution, the US created its factories, machinery, infrastructure, and most technology around the Imperial System. To switch to the Metric System would cost thousands and thousands of dollars and take years to switch.
So, the US stayed with the Imperial System while the rest of the world went Metric.
Converting kPa to psi
In order to relate these two units of pressure you use this conversion:
1 psi = 6,895 Pa = 6.895 kPa
kPa to psi Examples
Let’s look at an example conversion. Let’s say you have an industrial hose that releases water with a pressure of 2100 kPa. But you’re an American company, so perhaps you need to know that pressure in psi. This is how the conversion would look:
2100 kPa = 1 psi / 6.895 kPa = 304.6 psi
Let’s do one more example. You have an air compressor that can compress air in a range of about 413 kPa to 758 kPa and you want to know what that range is in psi.
413 kPa = 1 psi / 6.895 kPa ≈ 60 psi (59.9 psi exactly)
758 kPa = 1 psi / 6.895 kPa ≈ 110 psi (109.9 psi exactly)
So in this case, the air compressor would have a range of 60 to 110 psi.
psi to kPa Example
You can also use this same conversion to convert from psi to kPa.
For example, let’s say you know that a tire has a pressure of 33 psi. What does that equal in kPa?
33 psi = 6.895 kPa / 1 psi = 227.5 kPa
Depending on the application, you can convert between these pressure units.
Using kPa vs psi
As we said earlier, kPa is the unit usually used in scientific and engineering concepts and applications, as well as in most countries around the world. The kPa unit is used for scientific concepts like physics, engineering, and chemistry in all countries, including the United States.
The unit psi, on the other hand, is used all over the United States for most everyday applications and contexts like water pressure, blood pressure, tire pressure, air tank pressure, etc.
It’s also used in the United States for industrial concepts like pressure gauges, air compressors, hydraulics, and more.
You’ll often find many industrial parts list both kPa and psi units. However, conversions are helpful for industries that work internationally as well as for general application in various industries and industrial parts.
Both kPa and psi are valid units used to describe pressure. The one you use will depend on the context and the industry you’re working in.
The good news is converting from kPa to psi or psi to kPa is a simple calculation.
Curious to learn how these pressure units and pressure apply to industry? Check out our article on how hydraulic pumps can regulate and manage pressure in practical and actionable ways.