# The Weight of Air (and birds)

**Commonly pondered question:**

How much does all the air on the Earth weigh?

Make your predictions now: **a)** more than the Earth itself** ** 0 kg, air weighs nothing, duh** c)** More than all the birds on Earth ** d)** 7.89 kg

One cubic meter (1000 liters) of air weighs 1.292 kg (so if you chose d you are probably already wrong)

But that doesn't help us much, because as you go further up in the atmosphere, the density changes. The mass of the air is the same, but there is just less of it per cubic meter.

**Calculations:**

Another way to approach this problem: the air pressure at sea level is **14.7 psi**, in other words, all the air in a 1in x 1in area all the way up to the top of the atmosphere would weigh 14.7 lbs

***we'll convert to more physics like units later***

Now we need to find out the surface area of the Earth:

Earth's radius: 2.5E8 in (again we'll convert later)

Surface area of a sphere: A = 4*pi*r^{2} = **7.854E17 in ^{2} **

Now multiply: 7.854E17 in^{2} x 14.7 lbs/in^{2} = 1.155E19 lbs

All the air in the Earth's atmosphere weighs approximately: **5.3E14 kg**

**Compared to:**

All the birds on the Earth: net weight(very approximately) =** 3.6E12 kg **(if you chose c at the beginning, you win *suggest prizes in the comments*)

The Empire State Building(approximately) = **3.3E8 kg**

500 really big boulders(exactly) = **3.4E4 kg**

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