A PC consumes between 60 watts to 300 watts per hour.
A desktop computer use around 60 to 100 watts while not in use and just sitting idle and when you use the computer the PC uses around 150 to 200 watts.
If you're gaming or doing resource intensive tasks with the computer then the computer can use the whole 300 watts.
Most computers are built to use up to 400 kilowatts of electricity per hour, but they usually use less than that.
The average CPU uses about as many kilowatts per hour as the typical light bulb.
Any computer that's running on a Pentium-type processor uses about 100 kWh.
This is with the monitor off.
Laptop computers use around 50 to 65 watts of electricity.
The monitor of a desktop computer uses around 35 to 50 watts depends on how large the monitor is.
The old CRT monitors used around 100 to 200 watts of electricity per hour.
A gaming computer requires somewhere between 300 – 500 Watts to operate.
This translates to up to 1400 kWh annually and is six times higher than a laptop's power usage.
However, these figures vary, depending on the gaming PC features, such as the installed hardware and software and usage frequency.
These days whenever you try to buy/build a PC, you constantly see demands and suggestions for large power supplies.
400W seems to be for low-end machines, Real Men need at least 500W, but if you intend to do gaming, better get at least 650W, etc.