Power Supply Calculator Figures Out What Size PSU to Buy [Hardware]
Simply enter your CPU, motherboard, video card, and the rest of your components into the form, click the Calculate button, and you'll see an estimated wattage for the power supply you need to buy. As somebody who not only builds his own PCs, but wrote a whole series on how to build your own computer, I can tell you that when it comes to power supplies, you want to buy quality—don't cheap out or it will die very quickly.
For more, check out our beginner's guide to building a PC from scratch, or learn how to replace a dead power supply, install a motherboard and CPU, install a PCI card, or install RAM in your Mac and save a ton of cash.