"R.stol" writes:

fyi ,,, P=U x I aka Watt = Voltage x Current

That's for DC. AC requires considering the power factor.

,,, measure how much Current
the pump is taking ,, and mutliply it with your voltage.

Times the power factor gives the power..

For a 550 watts
pump the current should be mesured ~5 Amps on a 110 Vac leader.

However Measuing the Current is not going to be a easy task with that
instrument as you have to measure Current (Ampere) in serie with the Pump ,
there is however Ampere meters that you can simply clamp around the wire to
measure the Amps.

It has a series resistor.