What is the current level of oxygen on the planet?

Question

14%?

Answer 1

21-22%

Answer 2

21%

Answer 3

From Wikepedia it is 20.95%

Now when you quote a percentage of a gas, you need to mean as a percentage by weight or by numbers of molecules, ie by volume.

This is a percentage by volume.

We can readily survive with 12%. We might adapt to 6%... this might depend on how quickly the change happens.

Answer 4

The answers above are essentially correct, as is the 12% being a good threshold limit for oxygen concentration *at sea level*.  However, should the sea level oxygen concentration drop to 12%, or 0.12 atm, then higher-elevation cities like Denver and Mexico City would become uninhabitable since the oxygen concentration (in terms of absolute partial pressure), would be nearly below the threshold for survival.  

Curse you atmospheric physics!