Many of the calculators previously featured here no longer function on modern browsers, so we have moved them to the updated version here:

Have you, or someone you know, ever suffered from HAPE (high altitude pulmonary oedema)? If so, please visit the HAPE Database today to find out more, or click to register.

Altitude air pressure calculator

Click on the menu on the left to see the range of interactive calculators

At sea level there is a pressure equivalent to 10 metres of water pressing down on all of us all the time. This is because of the weight of the air above us in the atmosphere. When you travel up a mountain, there is less air above you in the atmosphere,

The important effect of this decrease in pressure is this: in a given volume of air, there are fewer molecules present. This is really just another way of saying that the pressure is lower. (This is called Boyle's law.) The percentage of those molecules that are oxygen is exactly the same: 21%. The problem is that there are fewer molecules of everything present, including oxygen.


At , the standard barometric pressure is kPa ( mmHg). This means that there is % of the oxygen available at sea level.

Click here to see the effects that this has on the body's oxygen supply.

Last updated: February 2018