Scientists work in

**SI Units**. For pressure this means newtons per square meter (Nm

^{-2}). SI units are named

after famous scientists and the pressure unit of 1 Nm

^{-2 }is named after

**Blaise Pasca**l, so 1 Nm

^{-2 }= 1 Pa

1 Pa is a tiny pressure equivalent to one newton (the weight of a small apple) over one square metre.

To keep life simple, the kilopascal (kPa)

^{ }is normally used.

###
1 kPa = 1000 Pa = 1000 Nm^{-2}
^{}

^{-2}

By a lucky coincidence 100 kPa is very close to the pressure of the atmosphere at sea level. That pressure is caused by over 10 km of atmosphere sitting on top of us.

### 100 kPa ≈ 1 atm (1 atmosphere)

Another name for 100 kPa is 1 bar, so

###
100 kPa = 1 bar ≈ 1 atm

The bar is a useful unit because it relates to normal atmospheric pressure. A tyre with 3 bar is 3 times atmospheric pressure.

In this unit we will use bar for the pressure in an aerosol can.

### Download our Aerosols and Pressure poster here

aerosols_and_pressure-poster.pdf