A lot of people who are new to building computers such as myself overestimate how much power they need for their whole PC. I want to ask Logan if he could make a video about it and explain how much we actually need.
Use this, or you can find many others online. Most of em' seem pretty accurate, but always add an extra 50watts to be safe.
Well there are online tool that can help give you a good estimate, but I would not recommend getting a supply that is almost exactly what you need. I recommend getting a supply that is 50W to 100W more than you need to give some headroom for aging and adding expansions.
Here is an online utility I use from time to time to calculate power:
http://www.extreme.outervision.com/psucalculatorlite.jsp
Theres a long answer, and a short one. Heres the short answer:
Low end PC with intergrated graphics, maybe a low end card = 500w at most needed
Mid range system with a mid-low range GPU (760-770) = 600w at most needed
High end system with a high end single gpu (770-Titan) = 750w at most needed
Ultimate system with high end GPU crossfire (2x 770-2x Titan) = 1000-1200w at most needed.
Thats just my opinion. Hope this helps :)
i generally calculate it part by part, rough estimate for the cpu, fairly precise wattage's for gpus can be easy to find, unless there's a shit load of fans and harddrives throw in 50-100w for all the bits
for a generic guidlines: most single gpu setups will run on 500w (though this was before the hawaii gpus came out, don't know about them), dual gpu 850w will be sufficient (or less depending on the cards), you don't see past that too often and then you might want to start calculating it out again
This. Just try to find the absolute max values for each major component. For me, that's my GTX 770 overclocked ~ 200W, my i5 4670k overclocked ~ 80-90W, hard drives, mobo, fans ~ 50 - 100W and that's pretty much it. Of course you want some headroom so add another 10 - 15%. A high quality 450W PSU would be able to power this setup, as long as it has enough amps on the +12V rail (another thing to consider when choosing a power supply). I actually measured my system at 100% load on both the GPU and the CPU and on the wall it took ~ 350W. 500W for single GPU and 850W for dual GPU is absolutely safe, even with an overclocked AMD CPU/GPU combo and their higher power consumption.
You are overestimating your general guide by a lot. Put your examples into the calculator that a couple people have posted here and see what they come up with. Also:
http://www.youtube.com/watch?v=LiWThqgFfI4
http://www.youtube.com/watch?v=ajiN9aVOv4A