Wattage calculator required?

[Agera One]

So, I'm turning on my PC/Laptop in some occasion.. I play heavy games for 30 min, watch HD movies, internet video stream for 15 min, render a video for other 15 min.. So, how do I know how much watts my PC/Laptop consumed for that hour? Any software?

 

[13thmonkey]

nope, but as a reference when gaming my 3570k + GTX580 consumes about 300W from the wall. So each hour of gaming is 1/3 of a unit = 3p (in the UK). Assume 80% of the full load power draw for gaming, and 25% for non gaming this would be a reasonable stab at an estimate.