Atmospheric pressure and barometric pressure are two of the most used terms when it comes to the study of weather. Are these two different things, or are they related to each other?
Since they are pretty similar and related, it’s a very common mistake that people seem to make. I think that phrasing it as “barometric pressure vs. atmospheric pressure” is a wrong approach.
So, I’ll rephrase the question: when do we call it atmospheric pressure, and when do we call it barometric pressure?
Well, that’s why we’re here. Let’s get rid of any confusion we might have.
What Is Atmospheric Pressure?
Let’s look around. What matter is present around us in the largest amount? Is it the soil? Or water?
No, none of that. It’s air comprising of different gases. That’s another subject for a different time. The air components have a total weight.
This weight is exerting itself on every surface on earth, from the soil to water, cinder blocks to every building. As we go up vertically, atmospheric pressure drops. And as we go down, the pressure also drops.
To understand atmospheric pressure, we need to understand the concept of pressure. Pressure is the force exerted per square of area.
This force exerted by the atmospheric air divided by the total surface is what we call atmospheric pressure. We all learned it in school. Atmospheric pressure has a unit called pascal in the name of the scientist behind its study.
We measure the atmospheric pressure in kilopascals. One unit of atmospheric pressure is equal to 100 kilopascals.
Atmospheric pressure is a close approximation of hydrostatic pressure caused by the weight of air. Hydrostatic pressure is the force exerted by a compressible fluid per unit of area.
How to Find Atmospheric Pressure in Your Area?
This is where things get a little confusing. We measure atmospheric pressure by using a machine called the barometer. It seems a lot like the barometric pressure we’re talking about. Don’t worry; we’ll sort it out.
To measure the atmospheric pressure of your area, you need a barometer. And the rest is easy. You need to know what the measurements mean.
If the unit shows 30.20 inHg or above, the weather will stay the same. If it’s less than that but higher than 29.80 inHg, then you’re looking at either a storm or light rain, depending on how it changes.
What Is Barometric Pressure?
Barometric pressure is the pressure reading that you get from a barometer. A barometer measures the atmospheric pressure, and you get it as a reading. There are no fundamental differences between the two. It’s just how you look at it.
It can be measured using many different barometers. One pretty common machine is a mercury barometer. It’s contained in a tube, and the increase in atmospheric pressure pushes it up. That’s the barometric pressure reading.
Watch this Ted-ed video if you still don’t understand how a barometer works.
Does barometric pressure affect humans?
Barometric pressure can have negative effects on humans. The most common effects are headaches (sinusitis and migraine) and arthritis. But it’s mostly experienced by people who are already diagnosed with them.
A difference in air pressure around the sinus can cause headaches, while arthritis patients will experience joint pain. The change in air pressure affects the joint fluids.
While that’s true, a change in barometric pressure has to be significant to have a noticeable effect. For example, scuba divers may experience discomfort when diving deep in the waters. The nitrogen dissolves into the blood in high pressure.
Coming up from the dive will cause gas bubbles in the blood, which are called the bends. These can sometimes be fatal.
On the other hand, if you go up from the sea level by doing activities such as climbing mountains, you’ll see a noticeable effect. It can cause nausea, shortness of breath, tiredness, etc. It should be looked at by a physician. If it’s left untreated, the symptoms may become severe.
How to Find Barometric Pressure in Your Area?
If you want to find barometric pressure, all you need is a barometer. It’s going to give you a reading based on the atmospheric pressure. A rising barometric pressure reading means increased atmospheric pressure, and a fall in reading means decreased.
You don’t have to use a mercury-based barometer either. Another good alternative is an aneroid barometer. Or if you want you can try a few DIY methods, such as the colored water barometer.
Here’s how to get a reading from a barometer;
Setting up the barometer will be different for different types of barometers.
For Aneroid Barometer
- Calibrate it to a local reading (if you’re not measuring pressure at sea level).
- To get the local reading, go to any reputable weather website and put your postcode.
- Using a screwdriver to set the local reading on your aneroid barometer.
- Set the indicator hand using the adjustment screw in the back to the local pressure reading.
- Do the same with its marking needle.
For Mercury Barometer
- After you’ve got a reading from your mercury barometer, use a conversion chart to adjust your barometer’s reading to your local reading.
- Using the conversion chart, you’ll calibrate your mercury barometer for your altitude.
- From the chart, you’ll get a correction factor. Add this factor to your barometer’s reading.
- The adjusted reading will match the local reading you got from a website or a radio weather forecast.
For Electronic Barometer
Electronic barometer is the most complex out of the three but the easiest to get the reading out of. It automatically calibrates itself. So, what you need to do is just get the reading from it.
Here’s a Few Cautions to Follow to Get Unaffected Readings:
- Put the barometer in an open room or area where air can pass freely
- Avoid AC rooms
- Mercury won’t work 1000ft above sea level
- Don’t place the barometer at a place where sunlight hits directly since temperature change will affect reading
- Avoid drifty areas such as windows or doors since the air pressure varies greatly in those places
For those who’re interested, here’s a pretty easy-to-follow tutorial on how to build a DIY barometer at home.
Barometric pressure and atmospheric pressure have both similarities and differences. One similarity is that if we move up or down from the sea level, both will increase and decrease parallelly.
Barometric Pressure vs Atmospheric Pressure: Head to Head Differences
So far, we have seen that these two terms aren’t exactly opposite of each other. What exactly is the difference between them? Here are a couple of points.
One Is Measured, and the Other Is a Measurement
The main difference between atmospheric pressure and barometric pressure is that atmospheric pressure is the amount of air pressure at a particular place. Whereas barometric pressure is the reading, we get from a barometer.
So, barometric pressure is the measurement of atmospheric pressure. And atmospheric pressure is measured by a barometer.
The Difference in Unit
Atmospheric pressure uses the unit of Pascal. The standard measurement is 101.325 kPa. And barometric pressure uses the unit of atm or bar.
Way of Measurement
Atmospheric pressure can be measured by barometer or using the water level. On the other hand, you get barometric pressure only when using a barometer to measure.
Frequently Asked Questions
What is the atmospheric pressure in kPa?
The atmospheric pressure is different everywhere. But the standard atmospheric pressure at sea level is 101.325kPa.
Is measuring pressure in absolute kPa or gauge kPa?
There’s no definitive way to say it. Atmospheric pressure is positive. But for the sake of describing a system under a vacuum, pressure can be expressed as absolute 80kPa, or gauge pressure of -21kPa (21kPa less than atmospheric 101kPa).
What is the normal range for a barometer?
At sea level, the normal range for barometric pressure is 29.2-30.8 in-Hg. It’s a rare sight that the pressure goes over 30.4 inHg. The highest recorded barometric pressure is 32 inches Hg.
Why do we not feel the atmospheric pressure?
We’re not feeling the atmospheric pressure because the surrounding atmospheric pressure is equal to the pressure inside our bodies. So, there’s no pressure difference. But as we go higher from sea level, we start to feel the pressure. That means we only feel comfortable when we are close to sea level.
Well, I think it’s pretty clear to you now that the phrasing of atmospheric pressure vs. barometric pressure is a wrong one. Instead, it’s all about how you look at things. They are the same but again different as well.
These two terms are related since they mean the same thing. We can use them interchangeably.
The important thing to remember about atmospheric pressure or barometric pressure is what they represent — the weather around us. Having a barometer in the house can be vital if you live in areas with chances of storms, cyclones, and other natural calamities.