But How can I safely measure and calculate my total watt used while playing a game?
(during these moments the VGA card will require more power)
It's already been mentionedhttp://www.newegg.com/Product/Product.aspx?Item=N82E16882715001&cm_re=kill_a_watt-_-82-715-001-_-Product
Highest wattage witnessed, multiplied by the typical efficiency of your power supply will give you a general idea of power use.
My system peaks at around 175w AC while surfing the net, average is around 150.
175 watts AC x.84 typical efficiency of my psu
147 watt load on the psu
Not 100% accurate , but about as close as you'll get without spending big bucks for testing equipment.