Anyone using this method of calculating % chance

[wdbaker]

All,
I read about this in a new book but can't remember the name.
To calculate percent chance of hitting one of your outs, you multiply the # of outs times cards left times 2
example: 4 flush on the flop, 2 streets to go, 4X2X2= 16% chance of hitting it. The author didn't claim that it was perfect but close of enough for calculation on the fly. What do you think and best way to convert to odds for comparison to pot. would it just be 100/6.25 ?

thanks
wdbaker