In nanometer scaled CMOS devices significant increase in the subthreshold, the gate and the reverse biased junction band-to-band-tunneling (BTBT) leakage, results in the large increase of total leakage power in a logic circuit. Leakage components interact with each other in device level (through device geometry, doping profile) and also in the circuit level (through node voltages). Due to the circuit level interaction of the different leakage components, the leakage of a logic gate strongly depends on the circuit topology i.e. number and nature of the other logic gates connected to its input and output. In this paper, for the first time, we have analyzed loading effect on leakage and proposed a method to accurately estimate the total leakage in a logic circuit, from its logic level description considering the impact of loading and transistor stacking.