Calculating Gas Density at Altitude: Simple Equation for Terminal Velocity

[MegaMan64]

Hi I have been reading a lot about how to calculate gas density and I am stumped. What I would like to know is how to calculate the gas density as apposed to altitude so I can use it in the terminal velocity equation found here http://www.grc.nasa.gov/WWW/k-12/airplane/termv.html
I would like to know if there is a simple equation that can calculate the gas density with only a few factors and not with dew point and other factors that I have seen in Meteorology.
Thanks for any help with this

 

[MegaMan64]

Hi I found an formula for calculating gas density at height it anyone needs it
p = 100 * ((44331 * 514 - z)/ (11880 * 516))
p is density and z is altitued in meters.