CFM Corrections

Hello,

I am trying to calculate the amount of exhaust coming out of an exhaust pipe.

I know CFM but I need to correct this number for exhaust temp and barometric pressure.

Exhaust temp = 441.2 F
Stack Diameter = 2.5 inch
CFM = 488
Barometric pressure = 30.01 in. hg

Here is my previous equation using PV inch H20
=((stack diameter/2)^2*3.1416/144)*(1096.2*(SQRT(PV inch H20/(1.325*(Barometric pressure/(Exhaust temp+460))))))

Any help would be appreciated thanks!