Power Ratio is the mechanical advantage of the winch and is calculated as follows:
length of handle x gear ratio radius of drum
The pull of the winch is based on the Power Ratio and not just on the physical size of the winch or the diameter of the drum. The Power Ratio is used to determine the load the winch may handle as follows: pull of handle (kg x Power Ratio = pull of winch (kg).
This means that by applying a load of 10kg, using a 10" standard handle, on a Power Ratio 40:1 winch, the winch can pull 400kg, assuming that the winch is 100% efficient. This is not possible in practice as the efficiency is reduced by internal mechanical friction losses.