That makes sense but I see a lot of places where they estimate power consumption in W or mWs. How do they do it? Is there may be a window of estimation possible

That makes sense but I see a lot of places where they estimate power consumption in W or mWs. How do they do it? Is there may be a window of estimation possible in a constrained environment? No network or file I/O I guess is all the restrictions we can put on a process without compromising functionality. Alternatively how do I measure power consumption of a random process? Assuming I only want to get a number and nothing else.