It's really simple to calculate the efficiency...
A machine is a device which turns one type of energy into another. The efficiency of any device is defined as:
Efficiency = Useful energy OUT / Total energy IN
You might not know the energy inputs and outputs of a machine, but you can still calculate the machine's efficiency as long as you know the power input and output:
Efficiency = Useful power OUT / Total power IN
You can give efficiency as a decimal or you can multiply your answer by 100 to get a percentage, i.e. 0.75 or 75%.