I just tested a pump at the shop.
Exactly 1 ml......
They must be pretty inconsistent because I have tested and got 1.5 before.
I have never got more than 1.5 out of a pump before though. And I know for 100% certain how much goes into the bottles is 120ml.
2 pumps at 1.5 should get you 40 days not 27 or whatever it was so Im assuming there is a wide inconsistency in the volume of 1 pump.