How to calculate the amount of thrust of a autogyro during auto rotation?
In auto-rotation, either flying level, or with a constant sink speed, the vertical component of the thrust provided by the rotor is exactly the same as the weight of the gyro...

In Wikipedia  https://en.wikipedia.org/wiki/Disk_loading#Momentum_theory  you can find the derivation of the following expression:

$T = 2v^2· A·  rho$

where T is the thrust of the rotor, v the sink speed in vertical auto-rotation, A the 'disk area' (that swept by the blades) and rho the air density.