can you tell me If in the given circuit .meas V(out)* I(load ) will give proper power value? Or do you have any other suggestions for the formula that can be used?Why .step? 1 cycle should be sufficient for measurement. The interval start and end should not coincide with a signal edge. You can do the measurement in waveform viewer if you set the plot limits to an integer multiple of cycles. But .measure statement will do well.