How do you generally calculate the total wattage of power supply needed for a system ?

Question

Any specific webpage that I can use ?

Answer 1

To calculate how much power your PC needs, total the wattage requirements for each of its components, and then add a safety margin of 30 percent.

Compare your total to your power supply's maximum wattage rating, which should be printed on the outside of its case. The rating can also be found in your PC's manual or on the vendor's Web site.

Power Lifts
To replace a power supply, first unplug the PC's power cord, ground yourself with a wrist strap or by touching a water pipe or other grounded object, and open the case. Disconnect the power supply's lines from the motherboard and other components, remove the screws holding it in place, and lift it out. Then reverse the process to install the new unit.

Answer 2

check each of your computer component's manual..