Power Usage

Is there a way to calculate power usage without a electricity usage monitor like a Kill-a-Watt? Also does anyone know the power consumption of this: Gigabye GTX 560 Super Overclocked  ? Thanks!

http://www.maximumpc.com/article/%5Bprimary-term%5D/gigabyte_gtx_560_super_overclock_review

305 WATTS??!?!?!?!?!?!?!?!??!?! So then I'm mining I'm eating 305 WATTS?!?!

The test is a overall power consumption

 ( 3.33GHz Core i7-975 Extreme Edition in an Asus P6X58D Premium motherboard with 6GB of DDR3/1333 and an 850TX Corsair PSU. The OS is 64-bit Windows Ultimate. All games are run at 1920x1200 with 4x AA.)

So if your running a amd sistem you can be pulling more on the 340w side in gameing 

I have no idea what mining pulls 

oh ok beacuse I read some where that it 'ate' around 150 watts load the card alone Thanks for the answer