How many frames are lost during loading?

[dufffader]

2 Frames for me in a Leica M.
When I load the film, I make sure the sprockets are engaged with the perforations on the film. Once the back is closed the the bottom plate screwed on, two full lever winds gets it ready to shoot. Works everytime on my M2 and M3.

This is a question I always had when trying to maximize the number of frames in a roll, and never managed to measure precisely. The question has become relevant again as I just accidentally opened my camera with a roll in:

Q: In a camera (say a Leica M) with a roll loaded, what is the distance between the exit of the canister and the end of the frame window? In other words, how many frames I need to move forward once I close the camera, so the next frame will not have been exposed yet? Anybody has measured?