# How to calculate atmospheric pressure?

• The Exestentialist
In summary, to find the atmospheric pressure, you need the mass of the atmosphere and the surface area of the planet. If you only have the percentages of each gas, it will not help you find the pressure. The equation for finding the pressure is to divide the weight of the atmosphere by the surface area of the planet. It is important to check the units and make sure to multiply by the acceleration due to gravity.

#### The Exestentialist

Let's say I had the composition of an atmosphere, the mass of the planet it was on, and the diameter/density of said planet. First, what else, if anything, would I need to find the atmospheric pressure? Second, what would the equation for doing so be?

You need the mass of the atmosphere.

DrStupid said:
You need the mass of the atmosphere.
By composition, I meant quantity of each gas.

The Exestentialist said:
By composition, I meant quantity of each gas.
If you know the total mass of each gas separately then you know the total mass of all the gasses put together.

If you know only the percentages (by weight) then what you know will not help you find the pressure you seek.

To get the pressure at the surface, which is usually referred to as the atmospheric pressure, just divide the weight of the atmosphere mg by the total surface area of the planet.

Chestermiller said:
To get the pressure at the surface, which is usually referred to as the atmospheric pressure, just divide the weight of the atmosphere mg by the total surface area of the planet.
In what units? I tried this with Earth's atmosphere and I didn't get the right answer.

The Exestentialist said:
In what units? I tried this with Earth's atmosphere and I didn't get the right answer.
What units did you use for the weight of the Earth's atmosphere and the surface area of the planet and what answer did you get?

jbriggs444 said:
What units did you use for the weight of the Earth's atmosphere and the surface area of the planet and what answer did you get?
I used 5.1x1018 kg for the atmosphere's weight and 4*π*12,742,0002 m2 for the surface area of the Earth. I got 2,499,684 kg/m2

The Exestentialist said:
I used 5.1x1018 kg for the atmosphere's weight and 4*π*12,742,0002 m2 for the surface area of the Earth. I got 2,499,684 kg/m2
Check your arithmetic and check your figure for the radius of the Earth in meters. I get around 11,000 kg/m2 on the back of an envelope.

Edit: 7 significant figures of computed output on an input that is only stated to 2 digits reflects more precision than is justified.

Radius. Sigh. I hate when I make stupid mistakes like that. Thank you all for your help.

The Exestentialist said:
In what units? I tried this with Earth's atmosphere and I didn't get the right answer.
Pa

jbriggs444 said:
Check your arithmetic and check your figure for the radius of the Earth in meters. I get around 11,000 kg/m2 on the back of an envelope.

Edit: 7 significant figures of computed output on an input that is only stated to 2 digits reflects more precision than is justified.
Don't forget to multiply by g.

Chestermiller said:
Don't forget to multiply by g.
I was assuming kilograms-force, but yes, I agree.

## 1. What is atmospheric pressure?

Atmospheric pressure is the force per unit area exerted by the weight of Earth's atmosphere above a given point.

## 2. How is atmospheric pressure measured?

Atmospheric pressure is commonly measured using a barometer, which measures the height of a column of mercury or other liquid in a tube.

## 3. What is the unit of measurement for atmospheric pressure?

The SI unit for atmospheric pressure is pascal (Pa), but it is often measured in other units such as millibar (mb) or inches of mercury (inHg).

## 4. How does altitude affect atmospheric pressure?

As altitude increases, atmospheric pressure decreases. This is because there is less air above a given point at higher altitudes, resulting in lower pressure.

## 5. How is atmospheric pressure calculated?

Atmospheric pressure can be calculated using the ideal gas law, which relates pressure, volume, temperature, and the number of gas molecules. It can also be calculated using weather data such as temperature and altitude.