Power Calculation

it depends on what you mean by "actual power". Do you want to know what the machine is using, or do you want to know how much it is putting out?

i want to know the amout of power it is consuming from the source

Re: i want to know the amout of power it is consuming from the source

Then you want the input power.

The power required (from the power source) is the input power.

You can gain a measure of efficiency by comparing it to the output power.

The difference is (waste) heat.

Considering an audio amplifier for a minute, if you need a certain amount of power to drive say a loudspeaker at a certain level of loudness, you need to consider the output power from the amplifier.

To know how much power the amplifier will need from the power source to develop that level of output power, you need to consider the input power to the amplifier.

That depend on what I want to calculate,

If you want to know, if a machine is sufficient enough to run a given load then you need to calculate output power, If you want to know if a machine can be driven on a given source then you need to calculate input power.

i dare say you must specify the input power. If that much power is not input, the machine cannot deliver the so called 'output power' can it ?