You can place a Power Probe from the Place menu, the Place Probe toolbar or the right-click menu on the schematic.

The power probe measures the power dissipated or generated by an analog component by summing the voltage and current product at each pin.

For DC and Transient simulations, the power probe calculates the instantaneous power according to the following formula:

Where V and I are the instantaneous values of voltage at each pin and current going into each pin respectively.

For AC simulations, the power probe calculates the complex power according to the following formula:

Where V and I* are the phasor values of the voltage at each pin and current going into each pin respectively. I* denotes the complex conjugate of the current phasor.

For example, consider this MOSFET:

The instantaneous power calculated by probe PR7 is:

P(PR7)=V(4)*I1+V(3)*I2+V(1)*I3

  Power readings for digital components are not supported.

  Use care when using the power probes because some components do not model the behavior of all pins. For instance, some opamp models do not use the V+ and V- pins and therefore the reported power will not be correct. On the other hand, some components have extra pins to model behavior that is not electrical, such as the thermal pins on this MOSFET:

Non-zero current into or out of such pins leads to an incorrect power calculation for the MOSFET.