How can I determine available power?

[Chryso]

Is there any way I can determine how much unused power is available on my system?
I would like to add another hard drive but I don't know if my system has enough available power.

 

[meltdown75]

You can use this link which is from johnnyGURU's power supply thread:

http://extreme.outervision.com/psucalculator.jsp

Lets you enter component setup and calculates recommended wattage.